09/24/2012 12:00 EDT | Updated 09/24/2018 09:25 EDT

Women born preemies have higher risk of complications when pregnant: study

TORONTO - Women who were born as preemies appear to have an increased risk of complications during their own pregnancies, a Quebec study suggests.

Researchers say the risk of complications such as high blood pressure, gestational diabetes and pre-eclampsia almost doubles for mothers who were born before 32 weeks, compared to women who were born full-term.

"We found that the more premature a lady was born, the higher the risk of having pregnancy complications," Dr. Anne Monique Nuyt, a neonatologist and researcher at Sainte-Justine University Hospital, said Monday from Montreal.

Using provincial medical and birth records, the researchers looked at 7,405 women born preterm and 16,714 women born full-term between 1976 and 1995 in Quebec. Of the preterm women, 554 were born at less than 32 weeks' gestation and 6,851 were delivered at 32 to 36 weeks.

Nuyt said among women born at less than 32 weeks, almost 20 per cent had at least one complication during pregnancy, compared with 11.4 per cent of women who were full-term babies.

"So it's nearly a doubling of incidence," said Nuyt, principal author of the study published Monday in the Canadian Medical Association Journal.

However, she pointed out that this type of research — known as an observational association study — cannot establish causality. In other words, it does not prove that a woman born prematurely or with a low birth weight will go on to have difficulties in her own pregnancies.

However, it does appear these women have an increased risk of complications, said Nuyt, calling the fact of being born premature a "new, not-yet identified risk factor."

While the mechanism that links a preemie mom with pregnancy complications in adulthood isn't known, Nuyt theorized there may be physiological changes related to a low-weight, premature birth that could set the stage for gestational diabetes or other complications.

The incidence of complications during pregnancy could also signal an increased risk of heart attack, stroke or Type 2 diabetes later in adulthood. "Some people consider pregnancy as an open window to the future of cardiovascular and metabolic health of a woman," she said.

Toronto obstetrician-gynecologist Dr. Joel Ray agreed, saying, "what happens in pregnancy is sort of a canary in the coal mine for a women's potential long-term health."

Ray, a clinician-scientist at St. Michael's Hospital, said women who get gestational diabetes often go on to develop Type 2 diabetes later in life. Meanwhile, pre-eclampsia, a condition in which there is a sudden spike in blood pressure and a spill of proteins into the urine, can herald a future heart attack or stroke.

Ray, who was not involved in the research, called the study innovative and well-done.

"What they did was give us a set of outcomes — high blood pressure or diabetes in pregnancy — that we know is a canary in the coal mine for adult onset diabetes or cardiovascular disease later in adulthood."

However, he offered another possibility as to why preterm and low-birth-weight mothers might be at risk for pregnancy complications: it may be that their own mothers were predisposed to have a premature birth due to high blood pressure, diabetes, tobacco use or because of certain ethnic backgrounds.

"So what we're seeing is the capacity for some of those features in Mom number 1 to be transmitted to her premature or small-for-gestation-age daughter," Ray said. "And then that daughter gets those same problems in pregnancy.

"It may have nothing to do with being born premature or being born too small, but rather that tendency to repeat history, the history of having a pregnancy affected by a condition that repeats itself in another pregnancy."

Nuyt said more studies are needed by a variety of research groups to tease out the answers.

Medical advances have meant that significantly more babies born before 32 weeks' gestation have survived over the last 30 years, compared with the past. Because some of those offspring are still in their teens and not yet having children, future studies may be able to reach stronger conclusions, based on larger numbers of women.

That could also mean a larger population will be at risk of high blood pressure, Type 2 diabetes and other related health issues, the authors say.

Still, Nuyt stressed the study's findings shouldn't alarm people.

"Certainly people should not be afraid of starting their family and of being pregnant. I think like anything else, being informed — and therefore in turn making sure the health professional that's taking care of you is also informed — is simply the key.

"And probably this might guide some tighter follow-up of making sure, for example, if there is a gestational diabetes, it is well-controlled."