There is a popular argument, often used by care provider’s to schedule inductions and cesareans, yet there is also an increase of misinformation and lack of proper evidence-based education around it too; this argument is about birthing big babies, also known as macrosomia.
Some professionals consider babies to be “big” when weighing 4000g at birth while others consider the limit to be 4500g at birth.
Babies born between 4kg and 4.5kg occur in roughly 9.1% of babies born to mothers without diabetes (type 1, 2 or gestational), in 11.1% to mother’s with gestational diabetes (before 39 weeks), and in 13.9% to mothers with type 1 or 2 diabetes (before 39 weeks). Evidence shows that women with diabetes who manage their condition and weight with adequate exercise and diet can reduce their risk of a macrosomia birth. So, figures for big babies being born are relatively low despite the high number of macrosomia predictions. Evidence also shows that a care provider’s suspicion of a big baby is 3 to 4.25 times more harmful than a woman who actually has a big baby without any suspicion (regarding induction, cesarean and maternal complication).
Big babies are most common with:
• Mothers who have any form of diabetes
• A genetic family history of consecutive big babies
• Male babies
• High BMI or excessive pregnancy weight gain
• Having had a previous macrosomia birth
1. Ultrasound Predictions
Are ultrasound predictions correct? The short answer here is actually ‘no’. In fact, evidence has shown that an ultrasound weight prediction/measurement is incorrect up to almost 80% of the time and can be off by up to 500g either way (in some cases it has been more than 500g) and also shows no difference in accuracy between 2D and 3D ultrasounds and MRI scans. In fact, only about 50% of the time, ultrasounds are actually correct in predicting a “big” baby. However, because ultrasound measurements are an unreliable source of factual information, permanent medical decisions shouldn’t be made on the basis of ultrasound results alone; it is considered unethical and your care provider should always inform you that ultrasound results for weight predictions are mostly ineffective and unreliable. This helps you to have clear communication with them while enabling you to make an informed decision for your birth. A trial of labour should always be a first and viable option before an induction or cesarean when birthing a suspected big baby.
2. Small Body or Pelvis
Evidence shows that a woman’s height and weight actually have no correlation to the size and shape of her pelvis and should not be used as medical evidence for an induction or cesarean. In fact, a truly small pelvis (also known as CPD, cephalopelvic disproportion) is actually rare and occurs in less than 1% of women, and even then, a high of 65% of CPD women have managed to give natural birth successfully. The most accurate way to assess if a woman truly has a small pelvis is with a trial of labour or with a physical exam and ultrasound measurement of the babies head. However, slow dilation or slow labour progress is often used by care providers as a CPD diagnosis, even despite both mom and baby being healthy and happy; this is not evidence based and can lead to greater risk for mother and child. Studies show that labour should be allowed to progress at it’s own individual pace if both mother and baby are not distressed.
An induction, like any intervention, carries its own risks and can increase your risk of a cesarean. An induction is not entirely necessary for a suspected big baby although evidence shows that early induction may reduce the risk of shoulder dystocia from 7% to 4%
4. Scheduled Cesarean Section
Evidence shows that approximately 3700 unnecessary cesareans would be needed to prevent just one case of permanent injury caused from shoulder dystocia. Cesareans carry many risks for both mother and baby and a trial of labour is recommended first as a safer alternative before considering a cesarean.
5. Risks Of Birthing A Big Baby
• SHOULDER DYSTOCIA: Evidence shows that only 7-15% of macrosomia babies actually struggle with this and most cases are handled safely with a trained care provider, generally an experienced midwife. Permanent nerve injuries due to shoulder dystocia only occurs in roughly 0.18% of babies and the biggest concern for care providers with this is legal litigation.
It’s imperative that you find a care provider who is well experienced in handling shoulder dystocia while also understanding the risks before deciding to sue, should complications result.
• UNPLANNED CESAREAN: Approximately 19.3% to 27% of macrosomia births end in cesareans.
• PERINEAL TEARING: Evidence shows that the risk of 3rd and 4th degree tears for macrosomia births was around 1.7% to 3% (vs 0.9% for non-macrosomia babies).
• POSTPARTUM HEMORRHAGE: Evidence shows that the risk of PPH for macrosomia births was 4.7% to 6% (vs 2.3% for non-macrosomia babies) and these cases are inconclusive when proving if PPH was due to the big baby itself or from the inductions and cesareans recommended by care providers.
• NEWBORN COMPLICATIONS AND STILL BIRTHS: Has varying evidence and can be viewed here.
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Below are some extra resources for your reading. I recommend you research your facts and options thoroughly and discuss the evidence with your care provider to make an informed decision for your birth.
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