General risk factors for premature births

One of the reports in this issue of TreatmentUpdate deals with a hormonal issue that appears to cause some HIV-positive women to give birth prematurely. Before delving into this report, we first provide some background about prematurity.

Most pregnancies in high-income countries are successful, with healthy babies being born. However, in some cases women may go into labour prematurely. In general, babies born prematurely need a high degree of care in specialized centres in hospitals so they can finish developing and be ready for life outside the womb without constant medical assistance. All of the factors that cause women to deliver babies prematurely are not known, but here are some that can increase the risk for giving birth prematurely:

  • diabetes
  • heart disease
  • kidney disease

Other risk factors include some of the following:

  • a premature widening of the cervix (called cervical insufficiency)
  • having a history of giving birth prematurely
  • urinary tract infections or an infection that affects the membranes surrounding the fetus
  • preeclampsia – a syndrome of higher-than-normal blood pressure and excess protein in the urine that can develop during pregnancy
  • poor nutrition
  • substance use, including tobacco and street drugs
  • reduced production of the hormone progesterone

It is important to know that in some cases doctors may not be able to find a cause for premature birth


The ovaries produce the hormone progesterone. It helps prepare the uterus for hosting a fertilized egg. Once this occurs and the physical connection between the fetus and mother—the placenta—develops, the placenta produces the bulk of progesterone during the remainder of pregnancy. Progesterone helps the fetus to grow and protects it from the mother’s immune system. This protection is necessary because the developing fetus contains a mix of proteins, some from the mother and some from a foreign source—the father. Ordinarily the mother’s immune system would attack material it senses as foreign or non-maternal. However, progesterone and other hormones produced by the placenta cause the mother’s immune system to tolerate the fetus.

Research with HIV-negative women has found that in some cases supplementation with progesterone can help reduce the risk of pre-term birth by as much as 45%.

The next report focuses on Canadian research on progesterone and premature birth among HIV-positive women.

—Sean R. Hosein


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