Pregnant and overweight

By Dr Joe Kabyemela, MD

Obesity is now firmly established as one of the foremost serious health issues facing mankind today. In this regard, pregnancy is not spared. Problems posed by obesity are encountered in pregnancy like in all other walks of life and here they pose unique challenges, not only for the pregnant mother but for her baby as well. We have already discussed in detail the effect of obesity on fertility but of-course many obese women do become successfully pregnant. Here we look at the issues encountered when a woman conceives whilst overweight or obese.

How bad is the obesity problem?

A fairly recent survey by the Department of Health showed that in England, over half (53%) of women aged 35 -64 years were either overweight or obese. The rate among younger women is thought to be higher. In the United States, the latest survey statistics show that between 16 and 33% of children and adolescents are clinically obese, that is, their Body Mass Index (BMI) is above 30. This is a rise from 5% in 1964 and the trend does not appear to be slowing. Over a third of women above 20 in the United States are obese. A survey in Australia in 2006 showed that 35% of women aged 25 – 35 years were either overweight or obese.

There is no question that this is largely a lifestyle issue. Eating too much of the wrong things and exercising too little. In fact, the rate of obesity in the United States is almost three times that seen in comparable societies in Western Europe in countries such as Denmark, France and Italy.

Overweight or obese in pregnancy

The risk of complications and poor outcome to pregnancy is increased among overweight and obese women. This is across the entire spectrum of pregnancy, right from pre-conception, through the antenatal phase, labour and delivery right up to the postnatal period.

Here are some of the issues:

Miscarriage: The rate of miscarriage is significantly increased where the woman is overweight or obese. This applies to women who have polycystic ovaries (PCOS) as an associated factor as well as those with normal ovaries. Miscarriage could also be recurrent. For women with polycystic ovaries, they are known to have a biochemical problem of insulin resistance. The use of medication such as Metformin has been shown to reduce the risk of miscarriage for this subset of obese women. Not all women with polycystic ovaries are overweight or obese.

Fetal anomalies: The rate of fetal abnormalities especially those of the neural tube is increased among women who conceive whilst overweight or obese. The greater the weight, the bigger the risk. Some studies have shown that the risk of neural tube defects such as spina bifida or anencephaly may be twice that in the average population. It is thought many of these women have undiagnosed underlying Type 2 diabetes and this is the main driver for the increased rate of fetal malformation.

Scan imaging difficulties: The use of ultrasound to assess the wellbeing of the fetus in the womb is an established part of antenatal care. The accuracy of modern ultrasound is very good. It is therefore unusual for most gross anomalies to be missed when a detailed anatomy scan is performed at the mid-way stage of the pregnancy (20 weeks). This is not always the case with an obese woman. The presence of excess fat tissue on the abdomen means the quality of the images obtained is not as good. This increases the risk of missing organ malformations especially those of the heart and even the spine.

Pre-eclampsia: An obese pregnant woman has more than twice the risk of pre-eclampsia compared to her counterpart with a normal BMI. For those who are morbidly obese (BMI of 40 and above), the risk is increased five-fold. Pre-eclampsia is a potentially serious pregnancy complication with increased risk of fetal morbidity and mortality. Hypertensive disease of pregnancy remains one of the leading causes of maternal death in the western world. Pre-eclampsia is discussed in more detail here:

Thrombosis: the risk of thrombosis and thrombo-embolism is significantly higher among obese pregnant women compared to those with normal Body Mass Index (BMI).

Gestational diabetes: About 1 in 20 of all pregnant women will be diagnosed with gestational diabetes. The majority of these will be either overweight (BMI 26-30) or obese (BMI above 30). Gestational diabetes may need to be managed using daily insulin injections. The rate of fetal morbidity is also increased with gestational diabetes. In the long-term, the mother has around 50% risk of developing Type 2 diabetes. However, the diagnosis of gestational diabetes could be used as the clarion call for her to address the issue of her weight to prevent these long term health problems.

Preterm delivery: There is an increased rate of delivery before Term and the associated problems of prematurity. This is largely due to the pregnancy complications discussed above. The risk of antepartum haemorrhage due to both placental abruption and placenta praevia is not increased.

Intrapartum: (during labour/delivery)…

Fetal distress: There is a higher risk of fetal distress with increased rates of intervention in the form of instrumental delivery or emergency caesarean section among overweight and obese women.

Large babies: The rate of having larger than average babies is significantly higher among obese women. This may, on the surface be seen as a non-issue. However, it does carry with it a risk to both mother and baby. It means the risk of birth difficulties is increased with potential problems such as third degree perineal tear, shoulder dystocia and injury to the baby during delivery. It also increases the risk of emergency caesarean section (discussed below).

Caesarean delivery: The rate of caesarean section is increased around three times for clinically obese women compared to those with normal weight. This is both planned (elective) and emergency caesarean section. During labour, poor progress requiring intervention is almost three-fold the expected rate. Caesarean section is more technically challenging when the woman is obese. The recovery from the surgery is slower, the risk of wound infection and even wound breakdown is higher and other risks associated with surgery are also higher.

Anaesthetic problems: The mother in labour may wish to have an epidural for pain control in labour. This is more difficult to site when the woman is obese and even when successfully sited it may not be fully effective. This can be quite distressing. Difficulties with siting regional anaesthesia (epidural or spinal) may mean, if a caesarean section is required, she may be forced to have a general anaesthetic. This too is associated with its own challenges with difficulty with intubation and increased risk of other complications such as aspiration.

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