Women who have chronic hypertension (high blood pressure) before pregnancy are at greater risk of pregnancy complications than women who are not hypertensive before or during pregnancy. An exhaustive study of almost a million pregnancies in 25 nations indicates the risk is growing as more young women are overweight or obese before pregnancy. Excess weight is strongly associated with hypertension.

The study, conducted by a team of researchers from King's College London in the United Kingdom (UK), pooled data from 55 studies conducted in the UK, the United States, across Europe, and elsewhere. The studies involved 795,221 pregnancies.

The mission of the research team was to determine if women experiencing high blood pressure before and during pregnancy had a greater risk of experiencing certain complications of pregnancy than women free of hypertension before and during pregnancy.

Pregnancy complications of concern included:

  • Admission to neonatal or special baby care unit
  • Cesarean-section delivery
  • Low birth weight (less than 2,500 grams / 5.5 pounds)
  • Perinatal death (fetal death after week 20, stillbirth, and death of the baby within one month of birth)
  • Preeclampsia
  • Preterm delivery (before week 37)

The research revealed that women with chronic hypertension were eight times more likely to develop preeclampsia than non-hypertensive women. They were also twice as likely to experience all the other negative pregnancy complications than women without high blood pressure.

In conclusion, the research team writes, "Chronic hypertension is associated with a high incidence of adverse pregnancy outcomes compared with a general population." This conclusion stresses the value of getting chronic hypertension under control before conception.

The research team suggests pre-pregnancy counseling for optimum health before and during pregnancy. They also acknowledge better strategies are needed to predict which women are at the greatest risk of adverse outcomes of pregnancy.

Between 1% and 5% of all pregnancies in the US involve a woman with chronic hypertension but the percentage is expected to rise due to changes in the health status of young women in the US. A separate study recently compared the incidence of chronic hypertension in 1995-1996 to that of 2007-2008 and found the number of cases of chronic hypertension is rising. It also revealed the rate of obesity and metabolic disorders — two factors known to adversely affect blood pressure — are also on the rise.

Source: Bramham, Kate, et al. "Chronic hypertension and pregnancy outcomes: systematic review and meta-analysis." BMJ. BMJ Publishing Group Ltd. Apr 15, 2014. Web. Apr 24, 2014.