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My name is Debby Miller. I am a thirty something mother of two boys. One born by caesarean and the other a VBAC. I work full time as a financial adviser in a Government Department and am currently studying two degrees Accounting and Human Resource Development. From my work and study I have developed a good ability to research things. A skill that was particularly helpful to me when I was researching for my VBAC birth. I have a great interest in birth issues, particularly related to being an informed patient because of my first bad birth experience and my subsequent good one. I have offered to write a series of articles about a variety of subjects for Birthrites in the hope that my experiences and investigative abilities can help other mothers and mothers to be to make informed decisions about their birth choices. The topics I intend to write about are shown in the Discussion Topics Index. I will not be writing them in any specific order or to any specific time frame. I would advise all readers to read the first article Believing What You Are Told as this provides the basis for you to understand how assessments are made, both by myself and in the references I use, on the remainder of the topics discussed. I will try to keep the articles simple and will provide examples where possible. If medical terms are used I will add them to the Glossary so you can see what they mean. I would ask that readers note that I will try to keep the research factual and not input my own personal bias, however whilst I am aware of my own prejudices, I will probably lean towards documentation that supports my view. Secondly I am not a medical practitioner, nor do I have any medical training. The information I present will be based on research, journal articles and texts, and my interpretation of those. I will quote all references. Women wishing to use the information I provide are recommended to read the references for themselves and should discuss any issues pertaining to their own medical management with a qualified medical practitioner or midwife. Macrosomia, CPD and Dystocia Big Baby and Small Pelvis Introduction So you have been told you are going to have a big baby. It might get stuck in your pelvis. Your practitioner is throwing around words like macrosomia, shoulder dystocia and cephalopelvic disproportion and highly recommending you have a caesarean, particularly if you are a VBAC or first time mother -- but is it really necessary? This article will look at two areas that are somewhat intertwined that is the large baby and the supposedly small pelvis. What is Macrosomia. Macrosomia is the term applied to large babies, it literally means large baby. What constitutes a large baby varies from doctor to doctor but most identify a baby as being macrosomic if the baby is over 4000 &endash; 4500g (about 8lb13oz &endash; 9lb15oz) at birth. (Ref 9) Why Are Some Babies This Big? There are two main reasons women have babies that are classed as macrosomic, these are the baby has big parents or the mother has gestational diabetes. Neither of these means that the woman will definitely have large babies it just means there is a greater chance she will. For example: I am 5ft 2in and my first son was 8lb 12oz and my second 8lb 1oz (2 weeks early). I was told they would both be over 9lb. A friend of mine is 5ft 10in. Her two children were 6lb 5oz and 7lb 1oz born!! As this shows some little women have big babies and some big women have little babies. So anyone any size can have any size baby, it is just that if you are big, or your husband is, you have a greater chance of having big babies. The same applies to gestational diabetes, a larger proportion of women with gestational diabetes have large babies &endash; but not all of them. (Ref 9&10) The other factor that can increase the size of babies is diet, particularly a poor diet high in sugar and fat. It is very important to both the mother and baby that the mother eat a sensible balanced diet, that way she will remain healthy and will have a healthy pregnancy weight gain, and the baby will receive all the right nutrients to grow and develop. How Can They Diagnose Macrosomic Babies? Measuring Baby. The two main ways that macrosomic babies are diagnosed is through manual calculation and ultrasound. Manual calculation is where the practitioner feels your tummy and guesses how big s/he thinks your baby will be. There have been no studies I could find that indicate how accurate practitioners are at estimating the babies size, their experience would certainly help however I would severely doubt the ability of any person to accurately predict between a baby that would not be classified as macrosomic at 3800g and one that is at 4100g. This is not a scientific method of estimating birth weight. Ultrasound is done by placing a scanning device called a transducer on the mothers tummy, sound waves are transmitted by the transducer through the mothers skin, the sound waves bounce off the baby and internal parts of the mother. The bounced back soundwaves are relayed from the transducer into a computer that creates a picture. This picture can be used to take measurements of the baby. Ultrasound is not enormously accurate. It has a sensitivity (chance of identifying) of 60% and specificity (chance of diagnosing those identified) of 90%. This sounds good but Rouse and Owen provide the following example of how this works in reality: In a hypothetical group of 100 women, 12 have babies over 4000g, these are macrosomic. Of the 12 babies who actually are macrosomic only 7 (60%) would be identified as such. Of the 88 who were not macrosomic 9 (10%, as 90% have been accurately measured) would be identified as macrosomic when they were not. This means that 16 babies would be identified as macrosomic. Nine of which are not macrosomic. There would also be 5 macrosomic babies who were not diagnosed as macrosomic. (Ref 12) So for the practitioner who wants to do caesareans for all macrosomic babies s/he would be performing nine caesareans on babies that are not actually macrosomic, (arguably nine unnecessary caesareans out of 100 women that's 9%!!), and there would be five babies born whose deliveries possibly might have needed closer attention. So ultrasound isn't really that accurate either. Reliability? Enkin Et Al state: 'Macrosomia can be assessed by ultrasound, but most formulae utilised to calculate fetal weight perform poorly in the larger fetus, and such estimates should be interpreted with caution' And How Does My Practitioner Know My Pelvis Will Be Too Small? Measuring You. The reason the doctor may wish to measure you is because s/he believes that the babies head (or shoulders) may not be able to fit through your pelvis, either because s/he thinks you are small or the baby is large or both. This condition, if it exists, is known a cephalopelvic disproportion (CPD). Cephalic means head so cephalopelvic disproportion means the baby's head is a disproportionate size (too big) to get through the mother's pelvis. (Ref 10) The two methods commonly used to calculate the size of the mother's pelvis is an observational assessment and pelvimetry. Observational assessment is where the practitioner looks at your pelvis, and possibly other body parts to assess the relative size of your pelvis. Some look at height and shoe size but whilst there is some correlation between these and CPD, it has not been proven with any accuracy scientifically. They may also do measurements either with their hands or some sort of measuring device of your pelvic outlet, and may also do a full internal examination. The problem with this is that there are four main areas where the baby can get 'stuck' in your pelvis and this method cannot assess all areas. In addition this method is also very inaccurate and subjective (open to personal opinion rather than scientific fact). Pelvimetry is a measurement of the pelvis using Xrays. This may be done with normal Xrays or by CT scan. Some practitioners send a mother for pelvimetry after she has had a caesarean baby for suspected CPD. The problem with doing this is it is very difficult to identify any disproportion when there is no baby's head to compare the pelvis to. There are average measurements of the four areas that are commonly used for assessing pelvic adequacy, but what these do not allow for the changes in and relaxation of the ligaments of the pelvis that occurs in pregnancy. Where the mother is still pregnant the same measurements can at least be compared to the size of the baby's head. However what it again does not predict is the stretching of the pelvic ligaments during the birth process and the ability of the baby's head to mould as it moves down the birth canal. Here is a real time example. I had my first by caesarean for fetal distress at 7cm. The doctor suspected CPD and sent me off for a pelvimetry a couple of weeks after the birth. My measurements came back a bit below average and given that my sons head was only 33cm my practitioner indicated there might have been CPD. Two years later I pushed out a baby with a 37cm head with a second stage of just over half an hour - - so much for the CPD theory in my case. Reliability? Enkin Et Al state: 'Neither Xray nor clinical pelvimetry have been shown to predict cephalopelvic disproportion with sufficient accuracy to justify elective caesarean section for cephalic presentations. Cephalopelvic disproportion is best diagnosed by a carefully monitored trial of labour, and Xray pelvimetry should seldom, if ever, be necessary' The Royal College of Gynocologists (UK) indicate that the 'acceptable' measurements in pelvimetry are, Sagittal inlet 11.0 cm Maximum transverse of inlet 11.5 cm Bispinous outlet 9.0 cm Sagittal outlet 10.0 cm. However they do indicate that this is a poor means of predicting future outcomes: 'However, a retrospective study9 has revealed that X-ray pelvimetry in the puerperium is a poor predictor of future obstetric outcome and its use is associated with an increase in the caesarean section rate. Obstetric outcome in a second pregnancy was studied in 331 women who had had a previous caesarean section and who had undergone X-ray pelvimetry. Of the 248 women considered to have an inadequate pelvis radiologically,7 172 underwent an elective caesarean section. A trial of vaginal delivery was planned in the remaining 76 because the obstetrician questioned the value of postnatal X-ray pelvimetry. Of these, 51 had a subsequent normal delivery and 25 an emergency caesarean section. In the 83 women considered to have an adequate pelvis, 61 had a normal delivery and 18 underwent an emergency caesarean section. In the women who were allowed a trial of labour, the proportion who had a vaginal delivery was not significantly different whether pelvimetry was adequate or inadequate.' (Ref 3) Cohen & Estner also site a number of studies that indicate the inaccuracy of pelvimetry and The Cochrane Review indicates: 'There is not enough evidence to support the use of X-ray pelvimetry in women whose fetuses have a cephalic presentation.' (Ref 15) And finally in the words of Tarik et al: 'Our study showed that CT pelvimetry increased the rate of cesarean delivery without any benefit in the immediate delivery outcomes. Therefore, the practice of documenting the "adequacy" of the pelvis by CT pelvimetry before VBAC should be abandoned.' (Ref 5) Is It any different for VBAC Mums? In a word NO. See the quote above from the RCOG &endash; UK and Terik et al. Possible Pelvimetry Dangers. Just before we leave the topic of Xray pelvimetrys, one thing that did appear with in many of the articles about pelvimetry was that caution should be exercised in the use of xrays on the pregnant woman. With standard Xrays there has been some correlation between pelvimetry and childhood leukemia in the children who were subject to this type of examination. This has not been shown to be the case with CT pelvimetrys. 'In an extensive survey of deaths from cancer among English and Welsh children, Alice Stewart and her co-workers at Oxford University found a statistical relationship between fetal irradiation and the incidence of cancer among children. The survey, perhaps the most extensive of its kind, covered most of the children who had died of leukemia and other cancers between 1953 and 1955. The data gathered by the investigators show that, among children under ten, the chances of dying from cancer are twice as great for those who were irradiated during the fetal stage.' (Ref 6) But My Practitioner Says I Have a Contracted or Non-Gynaecoid Pelvis. There are four pelvic types gynaecoid, android, anthropoid and platypelloid. What these terms describe is the shape of your pelvis. Most women have a gynaecoid pelvis and most men have an android pelvis, but either gender can have any of the four types. None of these types in a woman means she cannot have a vaginal birth because regardless of the shape of the pelvis if the pelvic outlet is large enough for the baby to pass through, and all other things being fine, there is no reason why the baby will not pass through. It just means that if she does not have a gynaecoid pelvis there is a risk she may have a smaller than average birth canal. 'The maternal pelvis size and type (android, anthropoid, platypelloid) will have an effect on the birth canal size and shape and the forces encountered on the emerging head and spine. Gynaecoid is the most favourable pelvis present in approximately half of females.' (Ref 1) There is a higher incidence of problems in the non-gynaecoid pelvis however given that Anderson states only about 50% of women have gynaecoid pelvis that means there are 50% who do not &endash; and we do not have a 50% caesarean rate anywhere in the world so this must mean the majority of the non-gynaecoid women have vaginal births. 'Very few women actually have a pelvis which is too small to accommodate the average fetus. Often, if a woman has been told she has a small pelvis based on a history of a problem in labour, it is the size/position of the passenger or the force of the powers that is actually the problem. There are, however, a very small percentage of women who have a truly small pelvis or a deformed pelvis due to birth defects, pelvic fractures, or developmental problems. One of the developmental problems, now very uncommon in developed countries, is pelvic deformity due to vitamin deficiencies during childhood......this problem is almost unheard of in countries where adequate nutrition is available. Women with scoliosis, or curvature of the spine, which is relatively common in developed countries, generally do not have a deformed pelvis.' (Ref 8). Of more concern in relation to pelvic development is if the mother has had some disease or injury that affects the bones and may therefore have affected a normal development of the pelvis. The main conditions associated with this are rickets, polio and pelvic fractures And My First CSEC Was For CPD. Diagnosing true CPD, as you have read above, is a very difficult thing. Even in women who are suspected of CPD for their first delivery around 75% go on to have a vaginal delivery the second time around, and many with babies larger than their first. It is more likely the 'CPD' in the first birth was as a result of malpresentation of the baby (it was lying a bit oddly) than true pelvic contraction. (Ref 10) And My Baby's Head Has Not Engaged. Engagement of the babies head is an indicator but is not indicative of a problem. In most first time mothers, but not all, the baby moves down and becomes engaged around 36 weeks. In mothers who have already had a baby this may not happen until well into labour. Assessing if the head is engaged can be no easy matter as interpretation can be affected by the mothers position and the shape and size of her pelvis. (See ref 14) Persistent non-engagement of the head once labour is established can be an indicator that the baby is either malpositioned or that the mother's pelvis is too small to accept THIS baby's head. However labour should be given every chance before the decision for a caesarean is made. Another personal example, in my 27 hour labour with my second son (a VBAC) his head did not engage until about an hour before he delivered, this was despite being upright for most of the labour and doing squats and positions that are supposed to help engagement. But it did eventually happen when HE was ready and he was born with no assistance. So What if My Baby Is Big&endash; Why the Concern? The main concern with macrosomic babies is there is a slightly higher risk of shoulder dystocia. Shoulder dystocia is where the babies shoulder gets stuck when it is either entering or in the birth canal. Shoulder dystocia occurs in about 1% of all vaginal deliveries. (Ref 9) When shoulder dystocia occurs there is a risk of temporary or permanent injury to the baby and a risk of injury to the mother. The most common injury to the baby is a condition called brachial plexus injury or Erbs palsy. This condition can be temporary or permanent. (Ref 9) Why the Difference Between Mothers With Gestational Diabetes and Those Without? Babies born to mothers with gestational diabetes tend to have a larger weight gain for the size of the baby than those whose mothers don't have gestational diabetes. This is because the way the mother metabolises her food when she has diabetes means there is more sugar available for the baby. This means that little babies (as in short babies) will tend to have a greater weight gain than a baby of the same length born to a non diabetic mother. The babies are born with more fat, and have that rounded look (you've heard the saying he was born looking like a 3 month old &endash; like that). This means that their little shoulders are also comparatively larger because of the extra fat deposited there. (Ref 10) In the non diabetic mother with a macrosomic baby there is a increased likelihood that her baby is big all over, that is the baby is longer and therefore has more space over which to distribute its fat. This means that its shoulders would be comparatively smaller and therefore less likely to get stuck. Think of it this way. Two women on is 5ft and the other is 5ft 10in. Both weigh 70kg. The woman who is 5ft takes a size 14 &endash; 16 dress the one who is 5ft 10in takes a size 10. What Is Brachial Plexus Injury ? The brachial plexus is a network of nerves that conducts signals from the spine to the shoulder, arm, and hand. Brachial plexus injuries are caused by damage to those nerves. Symptoms may include a limp or paralysed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand. Although birth injury is the most common cause of this condition, it can occur at any time. There are four types of brachial plexus injuries:
Neuropraxia is the most common type of brachial plexus injury. (Ref 2) Is there any treatment? Most brachial plexus injuries from childbirth are neuropraxia and heal on their own. Many children improve or recover by 3 to 4 months of age. Treatment for brachial plexus injuries includes occupational or physical therapy and, in some cases, surgery. (Ref 2) What is the prognosis? The site and type of brachial plexus injury determine the prognosis. For avulsion and rupture injuries there is no potential for recovery unless surgical reconnection is made in a timely manner through surgery. For neuroma and neuropraxia injuries the potential for recovery varies. Most patients with neuropraxia injuries recover spontaneously with a 90-100% return of function. (Ref 2) So What are the Chances of My Baby Having Shoulder Dystocia and Brachial Plexus Injury? There is a risk of shoulder dystocia and therefore brachial plexus injury regardless of the size of the baby. However the risk is slightly higher for macrosomic babies and higher again for macrosomic babies of mothers with gestational diabetes. (Ref 10) The table below demonstrates the range of statistics that are demonstrated for shoulder dystocia, BPI and BPI resulting in permanent injury. Note that the range is expressed as a high estimate (worst case) or low estimate (best case), the real figure probably falls somewhere between the two but this demonstrates the variability of outcomes in different studies. What this shows, for example, for any non diabetic mother (which most are) with a baby of below 4000g (which most are) the risk of her baby having a permanent injury from shoulder dystocia in birth is between on in 1061 and one in 666 667 or not very high.
*(2). The risk of brachial plexus injury to any infant who has had shoulder dystocia in their weight group for their type of mother. *(3). The risk of that brachial plexus injury leading to a permanent injury for babies. '…the vast majority of macrosomic infants delivered vaginally do not experience shoulder dystocia.' (Compare this to the risks of other pregnancy problems detailed in my previous article.) And What Is The Big Concern If My Pelvis Is Small? With the smaller pelvis there is once again the risk of shoulder dystocia explained above. In addition there is also a risk that the baby's head will not progress down the birth canal &endash; cephalo-pelvic disproportion or CPD. The symptoms of this may be a prolonged labour, failure to progress and in some cases fetal distress. Once failure to progress has been diagnosed, (and the mother given a chance to see if it is transient or not), a caesarean is usually performed to deliver the baby. This is not however a reason to have a caesarean for all your babies. In most cases CPD is associated with the baby entering the birth canal in an odd position, they literally get stuck. The next baby however will more than likely enter the correct way and has as much chance of being born vaginally as any other baby. Often women who have experienced CPD in one labour will go on to birth a bigger baby in their subsequent labour. (Ref 8, 10, 11 & 15) What constitutes CPD is also a contentious issue which makes it very difficult to compare one study to another. However in the study by Impey et al a very strict definition of CPD was used &endash; where cervical dilatation arrested after 5cm, was unresponsive to a Syntocinon drip, after active ditatation of 2cm or more in 2 hours, with fetal malpresentations or malpositions excluded. Of women who experienced this type of CPD 68% delivered vaginally in their next labour, some with bigger babies. (Ref 16) So What Should I Do? As with all things, and as I have said you need to assess the risks and identify which risk you want to take. There is a risk your baby may be macrosomic, there is a risk that if it is it may experience shoulder dystocia and there is a risk that if the baby has shoulder dystocia it may end up with a permanent injury. But these risks are low. The alternative is an elective caesarean section and there are risks in this to both you and the baby, but that is a whole other article. Gherman indicates that there would need to be 443 prophylactic (just in case) caesareans to prevent one permanent brachial plexus injury. That's a lot of potentially unnecessary caesareans. Rouse and Owen also put forth the same argument. These are doctors putting up strong arguments in the mainstream obstetric journals against prophylactic caesar for the macrosomic baby in non-diabetic mothers. Conway and Langer argue that prophylactic caesareans reduce the rate of shoulder dystocia by about half, with a significant increase in caesarean rates. However what Conway and Langer do not indicate is that all these extra caesareans put the mothers and babies at higher risk of mortality (death) and morbidity (injury) than the vaginal delivery would have, and that the aim is not to prevent shoulder dystocia but to prevent permanent injury to the baby or mother. Babies who experience shoulder dystocia can be delivered safely and without injury in the majority of cases, by practitioners with the right training, obstetricians, doctors and midwives. Conclusion The studies and texts investigated do not on a whole support the use of caesareans where the baby is thought to be macrosomic. The ones that did had major flaws in their arguments that were countered by other professionals, (notably Ghermans response to the Conway and Langer study). Studies that investigated the benefits of caesareans for suspected macrosomia indicated there was no improvement in newborn outcomes. (Ref 13). The same applies for suspected CPD. Means of assessing if a baby is macrosomic or not are not accurate, and neither are the means of assessing pelvic adequacy, and therefore should not be used for confirming either of these conditions with a view to recommending caesarean. Whilst the risk of injury to a macrosomic baby is slightly higher than to a smaller baby, particularly if the mother has gestational diabetes, the comparative risk is still very low, and permanent injury is rare. Again the risks of any permanent injury to CPD babies is extremely low, and the only true indicator of CPD is failure to progress in labour. Like all other things no part of pregnancy and labour is risk free but armed with the right information we can protect both our babies and ourselves. Discuss this information with your practitioner and decide what is right for you. References:
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