Big Babies: the risk of care provider fear

Isla Miller (and cheeks)

Big babies are normal in well resourced countries. Over 10% of babies born in the UK and Australia weigh 4kg (8lb 13oz) or more. Healthy well nourished women grow healthy well nourished babies. Genetic factors also influence the size of babies (big babies run in families); and each baby a woman has usually weighs more than the last. Babies also continue to grow at the end of pregnancy (because placentas continue to nourish them rather than switch off) – so a baby will be bigger at 42 weeks than they were at 40 weeks.

However, abnormal blood glucose levels (BGLs) – with uncontrolled gestational diabetes (GD) – can also cause a baby to grow big. Babies who are big because of high BGLs are a different shape to ‘normally’ large babies. In particular, their shoulders and chest are larger and fatter, and they are more likely to encounter complications at birth. Unfortunately, research into big babies usually combines the outcomes for GD babies with non-GD babies.

Estimating size

The only way to accurately assess the weight of a baby is to weigh them after birth. Clinical assessment ie. palpating and measuring pregnant bumps is incorrect more than 50% of the time (Chauhan et al. 2005). Even the best available method – measuring the baby’s abdomen with an ultrasound – only predicts the weight of the baby within 15% of their actual weight (Rossi et al. 2013). Therefore, lots of women are being incorrectly told that their baby is ‘big’. A US study found that two out of three women were told their baby was ‘too big’ based on ultrasound (Cheng et al. 2015). In this study the average birth weight of the group of babies suspected of being big was 7lb 13oz – ie. not big at all.

Birth complications?

Giving birth to a big baby is associated with an increased chance of particular outcomes – notice I am using the term ‘associated’ not ’caused’. The main complication associated with big babies is shoulder dystocia. The incidence of shoulder dystocia increases with the size of the baby. For example, it occurs with around 1% of babies weighing less than 3.9kg (8lbs 8oz), compared to 5–9% of babies weighing between 3.9kg and 4.5kg (9lb 9oz) (Politi et al. 2010). Other less likely complications associated with big babies are severe perineal tearing (0.6%) and postpartum haemorrhage (1.7%) (Weismann-Brenner et al. 2012). I have previously written about how to reduce the chance of these complications:

Care provider fear

However, research suggests that the complications associated with big babies may be due to interventions carried out when a baby is suspected to be big. Care providers are more likely to diagnose slow progress during labour and recommend a caesarean if they suspect the baby is big (Blackwell et al. 2009). Women who are told that they have a ‘big baby’, and are counselled about potential complications, are significantly more likely to choose a planned caesarean (Peleg et al. 2015). One study compared the outcomes of a group of women with suspected big babies with a group of women who unexpectedly gave birth to a big baby (Sedah-Mestechkin et al. 2008). Women who were suspected of having a big baby were three times more likely to have an induction or caesarean, and were four times more likely to have complications such as severe perineal tearing and postpartum haemorrhage. In this study there were no differences in the incidence of shoulder dystocia between the two groups.

Therefore, when a baby is suspected of being big, a woman has an increased chance of interventions during birth, and of experiencing complications caused by those interventions, even if the baby is not actually big. The perception of a baby’s size influences outcomes more than the actual size of the baby. 

Induction?

A Cochrane Review comparing induction of labour before 40 weeks for a suspected big baby with waiting for spontaneous labour, found that induction decreased the incidence of shoulder dystocia from 6.8% to 4.1%. However, the review also found an increased rate of perineal tearing in the induction group of 2.6% compared to 0.7% in the spontaneous labour group; and an increase in the treatment of jaundice for the baby (11% compared to 7%). The review also notes that “antenatal estimates of fetal weight are often inaccurate so many women may be worried unnecessarily, and many inductions may not be needed.” There are a number of risks associated with inducing labour (see this post and this post) that need to be considered against the potential risks of of birthing a big baby.

NICE guidelines and World Health Organisation guidelines both state that induction of labour should not be carried out simply because a baby is suspected of being big. Interestingly, Queensland Health induction guidelines do recommend induction if a baby is estimated to be big via ultrasound. Yet the Queensland Health gestational diabetes guidelines state that “estimation of fetal weight by clinical assessment or USS can have significant margins of error”.

Summary

The estimation of a baby’s size via ultrasound is inaccurate. The complications associated with big babies may reflect care provider fear and practice. International guidelines do not recommend induction for a suspected big baby. Women need to be given this information before agreeing to an ultrasound scan aimed at estimating the size of their baby. Once the ‘big baby’ label is applied it cannot be removed and may alter the birth experience and outcome.

About MidwifeThinking

Midwife and Academic
This entry was posted in birth, intervention, midwifery practice, pregnancy, uncategorized and tagged , , , , , . Bookmark the permalink.

7 Responses to Big Babies: the risk of care provider fear

  1. aisling armenanzas says:

    As always, wonderful! Thank you !!!

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  2. Cecile Wise says:

    The hospital wanted me to have an extra scan to confirm my baby was “big” so they could induce me early. I declined, I ended up needing to be induced but I was nearly 42wks, had a 9lb baby (4080gms) small tear and minimal bleeding. My mum had had two cesars and smallish babies at term, but once my nana (on my dad’s side) told me she and my Aunty (her daughter) had “large” babies 3.9kgs and above I was relieved, I was never really stressed about it but she gave me a “good excuse” to argue my case. Everyone kept tell me I’d go early because I was “so huge” turns out I just grow healthy babies- he was 55cm long too

  3. CornishDoula says:

    Love this article! My smaller baby was a hard birth, she was 3.005kg (6lb 10oz) and felt all elbows and knees 😉 labour was long and hard. My bigger baby was predicted (an emergency scan at 39+4) to be 4.819kg (10lb 10oz). I was terrified… the fear I went through that afternoon was immense. I went into labour that evening at around 11pm, she was born at 2am, labour was smooth and easy in comparison. She popped out a chubby 3.912kg (8lb 10oz) so a whole 2lbs heavier than her sister but also 2lb lighter than was predicted! I had no tearing, no pph and a really great recovery.

  4. Laura Cao Romero Alcala says:

    Thank you so much, brilliantly written!

    Laura

  5. celemay says:

    it seems to me that the biggest problem is the estimation of baby’s weighy…. Why doing that if there is much imprecision and that brings fear?…. baby’s weight is one variable and in itself it says nothing about the dynamism of childbirth. We should always ask two questions: big for whom? compare to what?… childbirth is a complex phenomenon and should not be analyzed and managed with a mecanical perspective… Using only one variable in ordre to make decision can cause more harm than good… may be we need to use more wisdom in our practice?

  6. Denise Hynd says:

    Thank you for another informative and positive blog around women’s ability to birth the babies they grow!

  7. I supported a woman to birth recently who had a beautiful 4.6kg baby girl. She was 42 weeks and 3 days gestational age. Mum had purposely avoided any US after 20 weeks as she wanted minimal intervention in her birth. She birthed like a goddess – strong, proud, fierce and beautiful. She did not experience a shoulder dystocia, probably due to the wonderful way she moved with her body and her baby in second stage to manage descent effectively and intuitively. She sustained no perineal damage (37cm head circumference) at all. I find it very disappointing every time I hear a woman has ‘a big baby on board’, my heart sinks in the knowledge that she has now been ‘tainted’ with the ‘big baby’ label. Given the poor accuracy of US to determine baby’s size we need to be extra careful to avoid labelling women and babies this way, and thereby giving women ‘the fear’ over their pending birth.

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