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A methodical quest to time the delivery of high-risk babies

August 19 , 2011

Jennifer Hutcheon’s career as an epidemiologist was sparked by questions from expectant mothers in the Fraser Valley.

 

Dr. Hutcheon, while working as a nutritionist, often found herself trying to counsel pregnant women with diabetes on how to manage their blood sugar through diet.

“I would go to the literature for answers,” she says. “But often there were none.”

Determined to answer the questions herself when no one else had done so, she went off to earn a doctorate in epidemiology and biostatistics at McGill University.

Upon arriving at UBC’s Department of Obstetrics and Gynaecology as a post-doctoral fellow, Dr. Hutcheon was party to a departmental discussion about the optimal timing of delivery for women with pre-existing high blood pressure.

It’s a question that hangs over every obstetrician dealing with higher-risk pregnancies, whether caused by maternal hypertension, obesity, advanced age or multiple births:  When does the risk of continuing the pregnancy, which could result in stillbirth, outweigh the risk of delivering the baby early, which could result in complications for the baby, especially respiratory problems?

There is no definitive data to guide the mothers or their physicians. Not surprisingly, clinical practices vary for mothers with pre-existing high blood pressure, with some physicians recommending delivery at 36 weeks, some preferring to await spontaneous onset of labour, and everything in between.

“You would just think that we would have a good answer for that somewhere,” says Dr. Hutcheon, who became an Assistant Professor and a Scientist at the Child and Family Research Institute in March. “But the studies just haven’t been done, because huge sample sizes are needed to study rare, serious outcomes like stillbirth or neonatal death.”

This time, however, Dr. Hutcheon — recipient of fellowship awards from the Canadian Institutes of Health Research and the Michael Smith Foundation for Health Research — had the skills and expertise to find the answer herself.

Using a decade’s worth of U.S. birth records, she was able to assemble a large enough collection of data of stillbirths (about two in every 1,000 deliveries) to make solid conclusions about the trade-off. Her analysis, published in November in the British Journal of Obstetrics and Gynaecology, revealed that the risk of stillbirth increases sharply in the 39th week, while the risk of complications decreases fairly dramatically between 36 and 38 weeks.

So delivering in the 38th or 39th week would minimize the number of stillbirths as well as the number of neo-natal complications and Caesarian deliveries. Her findings are now being applied at BC Women’s Hospital and Health Centre.

A month after that publication, Dr. Hutcheon published a study in the same journal on a far more uncommon condition, but one that had been encountered at BC Women’s — diaphragmatic hernia diagnosed in utero.

A previous large-scale study indicated that earlier delivery, at 37 or 38 weeks, would lower the rate of stillbirths among infants with that condition. But Dr. Hutcheon, using a different methodology, found that delivery at 39 to 40 weeks was associated with better outcomes.

“We don’t want to be changing practice so all of these babies are delivered at 37 weeks, when in fact it could be causing harm,” Dr. Hutcheon said. “Let’s wait until we get a proper answer to this question before making changes to clinical practice.”

REPRINTED WITH PERMISSION FROM UBC MEDICINE, SPRING 2011, VOL. 7, NO. 1, Page 8