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Research shows increased risk of pregnancy complications in overweight and obese women

August 5, 2011

By Patricia Nicholson

A new study indicates that women who are overweight or obese have higher risks of pregnancy complications, including gestational diabetes, preeclampsia and emergency caesarean delivery. They were also at significantly higher risk of giving birth to a very large baby or a stillborn baby. These risks increased with body mass index (BMI).

Researchers in Denmark used data from the Danish Medical Birth Registry to study 369,347 singleton pregnancies in Danish women from 2004 to 2010. Almost one-third of the women were overweight or obese: 21 per cent were overweight (BMI 25-25.9), almost eight per cent were obese (BMI 30-35) and four per cent were severely obese (BMI over 35).

Women in the overweight and obese BMI categories had significantly higher risks for several pregnancy complications and unfavourable birth outcomes.

Women who were overweight had 3.5 times the risk of gestational diabetes compared to women of normal weight. That increased to almost eight times the normal risk for obese women, and 11 times the normal risk for those who were severely obese.

Similarly, overweight women were almost twice as likely as normal-weight women to develop preeclampsia, a serious condition marked by high blood pressure and protein in the urine. Obese women had three times the preeclampsia risk of normal-weight women, and severely obese women had 4.4 times the normal risk.

Caesarean deliveries – especially emergency caesareans – were significantly more common among overweight and obese women. Overweight women were 41 per cent more likely to need an emergency C-section than normal-weight women, and obese women were 73 per cent more likely to need one. Severely obese women had more than double the risk of an emergency caesarean compared to normal-weight women.

The risk of having a very large baby (over 4.5 kilograms, or about 10 pounds) was 60 per cent higher in overweight women, more than doubled in obese women, and almost tripled in severely obese women, compared to women with normal BMI.

Risk of having a stillborn baby increased by 40 per cent in overweight women, 60 per cent in obese women and 90 per cent in severely obese women. However, stillbirth was a rare complication, affecting only 0.3 per cent of pregnancies.

Being overweight or obese did not appear to affect risk of thrombosis (blood clots), hemorrhaging or shoulder dystocia (when the baby’s shoulders get stuck during delivery).

The study authors concluded that being overweight or obese was a significant risk factor for pregnancy complications, and recommended trying to address excess weight and obesity during pre-pregnancy planning.

The study appears in the August 2011 issue of Obstetrics & Gynecology.


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  • A publication of:
  • Women's College Hospital