Placental Compensation May Affect Fetal Growth


QUEBEC CITY — Placental compensation may influence fetal growth in women with gestational hypertension, according to research presented at the annual meeting of the Society of Obstetricians and Gynaecologists of Canada.

“Pregnancies complicated by gestational hypertension and to a greater extent preeclampsia had significantly lower birth weight/placental weight ratios, compared with the controls at 38 and 39 weeks,” said Rebecca Cash, M.D., a resident in obstetrics and gynecology at the University of Toronto.

In the retrospective cohort study, Dr. Cash and her associates analyzed information on 12,422 term pregnancies (37–41 weeks) using data from the St. Joseph's Health Care, London perinatal database on births from Nov. 1, 1995 to November 1999. Singleton pregnancies complicated by gestational hypertension (1,084 cases), preeclampsia (144), or chronic hypertension (129) were compared with pregnancies in normotensive controls (11,065).

At 38 weeks, women with preeclampsia had significantly smaller babies than did controls (3,350 g vs. 3,520 g), whereas there was no significant difference in birth weight in infants born to women with gestational hypertension and controls.

“In preeclampsia, the reduction in the ratio indicates that the fetus is undergrown in relation to placental size, suggesting functional placental impairment,” Dr. Cash said.

Pregnancies complicated by gestational hypertension showed statistically significantly larger placenta weights vs. pregnancies in the control group at 38 and 39 weeks (692 g vs. 682 g, respectively), but not at 40 and 41 weeks.

Larger placenta size suggests there is a compensatory increase in placental weight for decreased function in gestational hypertension, which may influence fetal growth. “Abnormal placentation is thought to play a central role in the pathophysiology of preeclampsia,” said Dr. Cash. She added that this may have an effect on long-term outcomes, as findings of low birth weight and large placenta are independent risk factors for cardiovascular disease in adulthood.

In the study, gestational hypertension was defined as maternal blood pressure greater than 140/90 after 20 weeks' gestation without proteinuria. Preeclampsia was defined as maternal blood pressure greater than 140/90 after 20 weeks' gestation, accompanied by proteinuria or other end organ abnormalities. Chronic hypertension was defined as maternal blood pressure greater than 140/90 before 20 weeks' gestation.

Pregnancies complicated by diabetes, stillbirth, and congenital or chromosomal abnormalities were excluded from the analysis. Placental weights were routinely determined without trimming membranes or draining blood.

Dr. Cash's associate in the study was Rob Gratton, M.D., of the University of Western Ontario, London.

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