preterm birth

In a recent perspective piece published in PLOS Medicine, researchers discuss the use and effects of progesterone in preterm birth prevention.

Progesterone is a naturally occurring hormone that has many effects on a woman’s body. It begins its production during puberty and is one of the essential hormones responsible for regulating the menstrual cycle. It exerts its effects, even during pregnancy, where it is known to reduce irritability and immune responses of the mother towards the baby in the womb. These results are significant as they help the mother’s body proteins to recognise the baby in the womb as her child thus stabilizing the pregnancy and preventing an early delivery. It is for this reason that clinicians have been known to use progesterone as a preterm birth prevention drug in mothers who suffer from preterm pregnancies.

Pregnancies are deemed preterm when the baby in the womb has less time to develop within the mother. This usually happens when a baby spontaneously delivers from the womb of the mother three weeks before the delivery due date. Parameters measured in the mother beforehand can check whether the mother is due for preterm delivery. If susceptible mothers are detected, then preterm management procedures are started for the women in question. The mother is admitted and the baby in the womb is monitored. During this time, obstetricians all over the world have been known to give the preterm susceptible mother vaginal progesterone due to its suspected pregnancy prolongation effects.

However, despite extensive use and the endorsement of several expert guideline groups, progesterone is not a licensed drug for this purpose and indeed the evidence supporting its use is limited. A recent perspective piece in PLOS Medicine discusses the available evidence with specific reference to a recent study in the same journal that examined the effects of progesterone in preterm birth prevention.

The PROGRESS study recruited women who were at high risk of preterm birth. The participants self-administered 100 mg progesterone or a placebo vaginally from 20 to 34 weeks of pregnancy. The identities of the women were masked and the clinicians concealed the information regarding the drug that the administered to the women (progesterone or the placebo). The distribution of either drug to the recruited women was random.

The results of the study showed that the women taking progesterone had just as many preterm deliveries as the women without progesterone (women on the placebo). These results came as a surprise to the researchers who expected the rates of preterm birth to drop for the women who took progesterone. In their research, they sought to find out the reason for this result. They concluded that the women who did not receive progesterone already had high levels of progesterone produced naturally by the body which saturated all the progesterone receptors in the uterus. Therefore, the additional administration of vaginal progesterone would not have any additional effects, since there were no available receptors present in the uterus to react to the added drug.

Many expert guideline groups endorse progesterone. However, this study adds to a growing body of evidence indicating that vaginal progesterone may not be as effective as we thought for preterm birth prevention.

Written by Dr. Apollina Sharma, MBBS, GradDip EXMD

Reference: Norman JE, Bennett P (2017) Preterm birth prevention—Time to PROGRESS beyond progesterone. PLoS Med 14(9): e1002391.

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