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Penny, first time mum, family birth centre

June 4, 2020

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You’re having a big baby? So what!

April 29, 2019

My phone beeps and lights up, I have a text message. I look at the screen and get a little excited, it’s from a client (I love hearing from my clients). I open the text message nonchalantly and scan the first few lines. Then I get it. That feeling. Deflation. Sympathy. Anger......


Yet another client who is being told her baby is big and she must be induced early. It happens so often I just go to my sent items and send the same email with evidence-based articles, studies and birth stories from women who have birthed larger babies – or been told they were having big baby. I feel so mad at these care providers for not showing all the evidence. Of course the Mum is now worried. The Midwife or OB has probably rattled off all the things that could go wrong. And stories from friends, well people only tell you the horror stories of birthing big babies, right? This is doing the Mum no favours and putting a dampener on all her hard work and mental preparation for a calm and positive birth experience. So, this week after receiving my third text message from a disheartened Mum who is feeling to pressure to set a date, I set about finding all the current evidence I could on birthing big babies. Not to prove anyone wrong or get them to change their minds but so they have all the evidence and can make their own informed decision.


So how are estimates of our babies’ weights done anyway? Growth scans. While they can be necessary and provide valuable information when identifying a potential issue, estimates on fetal weight should be taken with a grain of salt. The Australasian Society for Ultrasound in Medicine has a Statement on Normal Ultrasonic Fetal Measurements which states:


“No formula for estimating fetal weight has achieved an accuracy which enables us to recommend its use.”


Say whaaaaaat! Then why is it being used as the reason to suggest an induction? Well because of all the dangers of course. You know, you’re quite a small person and with such a giant baby inside you, you will most certainly have complications. Here’s a great fact – pregnant pelvises are not fixed structures! Our pelvis and connecting muscles, tendons, ligaments all stretch and open, ready to accommodate our baby. Pluuuus, our baby’s head is DESIGNED to mould perfectly to fit down the birth path. The bones in a baby’s are not fused together like ours are. This means the bones can move, and even overlap as they are born. You know that squishy bit on top of a baby’s head that you shouldn’t push, that’s the fontanelle. Bub’s bones will slowly fuse together over time and the fontanelle will get smaller and smaller.


Image: K Reeder


Ok, ok so the baby’s giant head can come through but hang on, it must have really broad shoulders too so you might get shoulder dystocia. Well let’s see what the Royal Australian and New Zealand College of Obstetricians and Gynaecologist’s (RANZCOG) guidelines on Shoulder Dystocia says about it shall we. Section 4.1, Can Shoulder Dystocia be Predicted?


“There is a relationship between fetal size and shoulder dystocia, but it is not a good predictor: partly because fetal size is difficult to determine accurately, but also because the large majority of infants with a birth weight of ≥4500g do not develop shoulder dystocia. Equally important, 48% of births complicated by shoulder dystocia occur with infants who weigh less than 4000g.

Clinical fetal weight estimation is unreliable and third-trimester ultrasound scans have at least a 10% margin for error for actual birth weight and a sensitivity of just 60% for macrosomia (over 4.5 kg). The use of shoulder dystocia prediction models cannot therefore be recommended”


So almost HALF of all cases of shoulder dystocia occur in babies LESS than 4.0kg! (Yes, you read that right). It goes on to say that early induction of labour for women with a suspected large baby, who do not have gestational diabetes, does not improve maternal or fetal outcome!


Image: Ben Bradfield



Let’s not stop here. Evidence Based Birth evaluated several studies on inductions and caesareans for suspected big baby.  You can read the full report here but to summarise:


“Women who were suspected of having a big baby (and actually ended up having one) had triple the induction rate; more than triple the Caesarean rate, and a quadrupling of the maternal complication rate, compared to women who were not suspected of having a big baby but had one anyway. There were no differences in shoulder dystocia between the two groups. In other words, when a care provider “suspected” a big baby (as compared to not knowing the baby was going to be big), this tripled the Caesarean rates and made mothers more likely to experience complications, without affecting the rate of shoulder dystocia (Sadeh-Mestechkin et al. 2008).”

“These results were confirmed by another study published by Peleg et al. in 2015. At their hospital, physicians had a policy to counsel all women with suspected big babies (suspected of being 8 lbs., 13 oz. and higher (≥4,000 grams) about the “risks” of big babies. Elective Caesareans were not encouraged, but they were performed if the mother requested one after the discussion. There were 238 women who had suspected big babies (that ended up truly being large at birth) and were counselled, and 205 women who had unsuspected big babies (that ended up being truly large at birth) who were not counselled.

Despite the fact that the babies were all about the same size, only 52% of women in the suspected big baby group had a vaginal birth, compared to 91% of women in the non-suspected big baby group. This increase in Caesarean rate in the suspected big baby group was primarily due to an increase in the mothers requesting elective Caesareans after the “counselling” session about big babies. There was only one case of shoulder dystocia in the unsuspected big baby group, and two cases in the suspected big baby group. None of these babies experienced injuries. There was no difference in severe maternal tears between the two groups.”


You’re feeling ragey too now right? If fetal weight is unable to be predicted with great accuracy and is not recommended and the evidence shows the instances of shoulder dystocia doesn’t increase significantly with a larger baby but mums have a higher chance of complications with an induction, then why in the world are they being offered?


So what can you do if you’re in this situation? Ask questions! Ask your Care Provider to show you evidence that supports what they are suggesting. Print out the RANZCOG Shoulder Dystocia Guidelines, the Statement on Normal Ultrasonic Fetal Measurements and all the studies below and take them to your next appointment and talk through them together and come up with a decision that you have helped to make.





ACOG - prevention of primary caesarean delivery 

“Caesarean delivery to avoid potential birth trauma should be limited to estimated fetal weights of at least 5,000 g in women without diabetes and at least 4,500 g in women with diabetes. The prevalence of birth weight of 5,000 g or more is rare, and patients should be counseled that estimates of fetal weight, particularly late in gestation, are imprecise.”


Science Daily - Perceptions of fetal size influence interventions in pregnancy

“Nearly one-third of women, without a prior cesarean, reported that they were told by their maternity care providers that their babies might be ''quite large," leading to higher rates of medically-induced labor or planned cesarean deliveries that may not be warranted, a new study co-authored by Boston University School of Public Health and Medicine researchers shows. The study in the Maternal and Child Health Journal found that only a fraction (one in five) of the expectant mothers who were told their newborns might be large actually delivered babies with excessive birth weights -- a condition known as fetal macrosomia, or a birth weight of more than 8 pounds, 13 ounces.

But those who were told that they had a "suspected large baby" had higher odds of perinatal interventions, regardless of actual fetal size. Women thought to be carrying big babies were nearly five times more likely to ask for cesarean deliveries, twice as likely to try to self-induce labor, and twice as likely to have medical inductions as other women, the study found.”


Suspicion and treatment of the macrosomic fetus: a review.

“CONCLUSION: Due to the inaccuracies, among uncomplicated pregnancies suspicion of macrosomia is not an indication for induction or for primary caesarean delivery.”


Labor and Delivery Experiences of Mothers with Suspected Large Babies.

“CONCLUSIONS FOR PRACTICE: Only one in five US women who were told that their babies might be getting quite large actually delivered infants weighing ≥4000 g. However, the suspicion of a large baby was associated with an increase in perinatal interventions, regardless of actual fetal size.”