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Pharmacy and Medications

Aspirin During 3rd Trimester of Pregnancy



Hi guys, I wonder why Aspirin can cause prolonged delivery of child and risk of bleeding if a pregnant woman takes this medicine during the last 3rd trimester of the term even she takes it correctly. From what I understand, this medicine doesn`t stay so long in the blood so its effect should wane a few days after the last dose. Does this medicine alter metabolism or physiology of a pregnant woman or does the pregnancy alter this medicine so that it effect the length of time for delivery as well as the risk of bleeding?


It is correct that aspirin is not recommended for general use by women in their third trimester of pregnancy. The reasons for this recommendation is that aspirin can increase the risk of bleeding, prolong or delay labor, and can cause a reroute of blood flow in a baby before its born in the later stage of pregnancy.

It is also true that the effects of the aspirin only last 1 to 3 days. Since the start of labor cannot be predicted, it is best for women to avoid use when they are at highest risk of going into labor such as during the third trimester. Also some of the reasons why people commonly take aspirin such as for back pain may be early signs of labor in pregnant women.

The affect of aspirin on pregnant women are not different than other people. Aspirin may interfere with the body’s ability to clot and stop bleeding in anyone taking it. Woman in the third trimester are warned against aspirin use because they are at higher risk of experiencing labor and delivery where bleeding can occur.

Aspirin also blocks the creation of what are known as prostaglandins in people. Prostaglandins are signals that have many effects on the body. Some of these are signals are sent to help start and continue labor. So aspirin use may prevent labor from starting or from it being as effective while the medication is still in the woman’s body. This can cause longer labors and deliveries in women who took aspirin shortly before labor started.

Aspirin may alter the physiology of the baby in the later stages of pregnancy before it is born. A drop in prostaglandins starts a natural process where blood starts to flow to the baby’s lungs. Normally this natural process is supposed to occur after birth when the baby starts using its lungs. But since aspirin blocks the creation of prostaglandins, it could cause this process to occur before the baby is born. This could cause fatal problems in the baby.

Sometimes women are told to use aspirin in their pregnancy by their doctor for certain conditions when the benefits are deemed greater than the risks, but these women and their babies are being monitored by their doctor. Pregnant women should talk with their doctor or pharmacist about what over the counter medications they recommend before taking anything.

Submitted by Kelly Jackson, PharmD Candidate
The Ohio State University College of Pharmacy

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Response by:

Carmen M Hadley, RPh, CSPI
Former Clinical Instructor
College of Pharmacy
The Ohio State University