Aspirin, a common fever, pain-relief and anti-inflammatory medication, is not recommended in adult doses (325mg) in pregnancy for their potential harmful outcomes both for the mother and baby. Despite the recent studies stating possible positive effects of the medication, it is never recommended to take aspirin in pregnancy without consulting your doctor .
Category C: In the first and second trimesters
Category D: In the third trimester, when taken in full adult dosage 
According to a warning issued by the FDA in 1990, the use of aspirin in adult doses is especially contraindicated in the third trimester due to increased risk of complications during delivery and serious birth defects in the baby .
Full doses of aspirin, especially in the last trimester, increase the chances of fetal and maternal bleeding by changing the body’s blood clotting actions .
Use during conception and in early pregnancy:
In late pregnancy:
High doses have been found to increase the danger of:
Baby aspirins contain about a quarter or even lower doses of aspirin compared to the adult doses, with each tablet containing 75mg to 81mg of aspirin . The low dosage might be prescribed by doctors in specific high risk pregnancies with increased chances of miscarriage, premature birth and preeclampsia .
Recent studies show low dose aspirin treatment can be beneficial for those diagnosed with anti-phospholipid syndrome (APS) or Hughes Syndrome. APS is known to increase the risk of developing blood clots, considerably increasing the chances of miscarriage. Taking prescription baby aspirin along with the anticoagulant medication heparin helps in preventing the formation of blood clots, thereby reducing the risks of miscarriage.
A 1990 study performed in Rotterdam showed the potential benefits of low dose aspirin in reducing the complications resulting from high blood pressure. Four trial doses in 122 pregnant women having high risks of preeclampsia (a history of the complication, obesity, being over 35 years of age etc.) showed a significant drop in their blood pressure, reducing their chances of kidney damage as well as the need for a c-section or inducing labor before the 37th week .
These results led to the Collaborative Low Dose aspirin Study in Pregnancy (CLASP), another similar research with a wider statistical sample including 9364 pregnant women for comparing 60mg daily doses of aspirin with a placebo for preeclampsia prevention (or early treatment). The results showed the low dose medication to reduce the risks of preeclampsia only by 13% overall. The statistics were higher in cases where the treatment began before the 20th week. The treatment also had possibly promising results in preventing fetal growth retardation and premature delivery [12, 13]. Women having a kidney disorder, hypertension, insulin-dependent diabetes or systemic lupus erythematosus may also benefit from the use of low dose aspirin along with regular monitoring.
The relative benefits and risks of the medication are still under research. Studies are being carried out regarding aspirin’s role in helping in conception in women with a history of a recent loss of pregnancy. However, there is still a lack of conclusive evidence in this regard.
Doctors may prescribe Paracetamol (Tylenol) for treating fever and pain in pregnancy as a relatively safer option with lesser adverse effects . However, it is never recommended to use any kind of medication without expert medical consultation.
Use of the medication in lactating mothers is not recommended as the drug enters breast milk and may lead to various adverse effects in the nursing infant . Consulting your doctor is recommended regarding whether to stop using the medication or to discontinue breastfeeding, depending on the necessity of the drug for the mother .