Researchers from New Zealand discovered that women who did not sleep on their left side the last night before delivering their babies had twice the rate of stillbirth compared with those that slept on their left side. It’s commonly recommended for pregnant women to sleep on their left side, especially later in pregnancy. There are various explanations for why this is preferred, from placing less pressure on the mother’s major blood vessels to worsening the mother’s snoring.
I’ve mentioned before that a woman’s risk of developing obstructive sleep apnea increases as she gains weight during pregnancy, but progesterone counteracts this effect neuromuscularly, by tensing the throat muscles and increasing the drive to breathe. However, back sleeping is a known aggravator of breathing pauses during sleep due to gravity’s effects on the tongue. Whether or not this leads to apneas (10 seconds or longer pauses), the mother will still stop breathing and wake up more often during the night. This can place a major stress not only on the mother’s body, but on the baby as well.
This study was an observational study, so more prospective studies are needed. But it only goes to show that any additional situation that can aggravate sleep-breathing problems during pregnancy can raise your risk of complications, which also includes gestational diabetes and preeclampsia.
I wonder if the researchers asked the women what their preferred pre-pregnancy sleep position was. I suspect that women who can’t sleep on their backs may have more complications during pregnancy due to narrowed upper airway anatomy.