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A new Lawson Health Research Institute study published in the journal Placenta has found a unexpected difference in the impact of pre-existing diabetes versus gestational diabetes on oxygen flow in the umbilical cord during pregnancy. 

Currently, tests done very close to the end of a high-risk pregnancy can’t reliably measure the full health of the placenta and baby. Women with complications like diabetes, high blood pressure and an elevated BMI (body mass index), among others, are therefore generally advised to induce labour before the 40-week mark.

“This study explored some of these high-risk pregnancies to better understand what occurs or changes in the placenta with the goal of eventually developing better tests,” says Dr. Barbra de Vrijer, High-Risk Obstetrician and Head of Maternal Fetal Medicine at London Health Sciences Centre and Scientist at Lawson. 

The St. Joseph’s Health Care London Perinatal Database, containing information on nearly 70,000 births between 1990 and 2011, provided the data for the study, including birth weight, placental weight and umbilical cord oxygen levels.

The study found that the number of blood vessels in the placenta (called vascularity) likely impacts oxygen in the umbilical vein, causing a slight increase in mothers with gestational diabetes, but a decrease in those with pre-existing diabetes.

Surprisingly, this new research indicates that hyper-vascularity in diabetic placentas (too many blood vessels) may actually decrease oxygen transfer, potentially leading to more risk to the baby.

“When there is an increase in placental vascularity, crowding of the blood vessels can occur constraining their effective absorbing surface area for oxygen uptake from maternal blood within the placenta,” says Dr. Bryan Richardson, Scientist at Lawson. 

Another finding of the study confirmed earlier research showing that in women with both pre-existing and gestational diabetes, who tend to have larger babies, the placentas were also disproportionately larger, which is an indicator of decreasing placental efficiency, or the birth to placental weight ratio.

While additional research is needed, Dr. de Vrijer sees hope in the development of newer tests that look at factors like metabolic markers – the results of which could help indicate if the placenta is insufficient and assist in decisions like whether and when to induce labour.

“There are new technologies that we are looking at studying moving forward,” says Dr. de Vrijer. “Our team is focused on continuing our research to better understand high-risk pregnancies with a goal of continuously improving care for pregnant individuals.”