Macrosomia is the medical term for a newborn baby who weighs more than 8lb 13oz. Macrosomia can make a vaginal birth difficult and can increase the risk of shoulder dystocia and a severe perineal tear.
Average birth weight for a newborn baby
In the UK, the average weight of a newborn baby is 7lb 8oz. A baby who weighs more than this is considered larger than average, and a baby who weighs 8lb 13oz or more is deemed ‘macrosomic’. Macrosomia translates as ‘big body’.
It is estimated that around 11% of babies in England have a birth weight of 8lb 13oz or more. Around 1.6% weigh 9lb 15oz or more.
Can a big baby be predicted?
It is quite difficult to predict whether or not a woman will give birth to a big baby. Ultrasound scans can provide some guidance, although these are not entirely accurate in terms of establishing birth weight.
It may become apparent that someone is going to have a large baby if the fundal height is greater than normal. The fundal height is the measurement from the top of the mother’s uterus to the pubis. A midwife will take this measurement throughout the pregnancy. If a woman is measuring very large for her dates, it can be an indication that the baby is going to be big.
There are other factors that increase the possibility of macrosomia, including:
- Diabetes/gestational diabetes
- Excessive weight gain during pregnancy
- Being more than two weeks past the due date
- Excessive weight gain between pregnancies
- Previous history of macrosomia
Macrosomia is also more common amongst Hispanic women, and amongst those who give birth to boys.
Complications of giving birth to a large baby
Giving birth to a larger than average baby can enhance the risk of certain complications. Most notably, a large baby can become stuck behind the mother’s pubic bone, a problem called ‘shoulder dystocia’.
There is also a risk of heavy blood loss and a severe perineal tear – meaning a 3rd or 4th degree tear. A tear can happen as a result of shoulder dystocia. Alternatively a tear can happen as an isolated incident, caused by the fact the perineum cannot stretch far enough to accommodate the delivery of the baby.
Should I have a C-section instead?
If there is a strong suspicion that a woman is carrying a larger than average baby, medical practitioners must decide upon the safest course of action. It may be advisable to induce the labour early, or book an elective C-section. This can minimise the risk of complication and avoid the possibility of an emergency caesarean.
If medical practitioners fail to act upon the warning signs of a large baby and a woman sustains a severe perineal injury, questions must be raised as to whether an acceptable standard of care has been provided. If not, there may be grounds for a claim. Contact us for more information.
