During which trimester do the majority of pregnancy losses occur?

The majority of pregnancy losses occur during the first trimester. This period, which encompasses the first 12 weeks of pregnancy, is critical for embryonic development, and it is also when approximately 80% of miscarriages happen. Factors contributing to these early losses often relate to chromosomal abnormalities, hormonal imbalances, and other health issues in the mother, making the first trimester a vulnerable period for fetal development.

As the pregnancy progresses into the second and third trimesters, the likelihood of miscarriage dramatically decreases. While losses can and do occur in these later stages, they are significantly less common compared to the first trimester. The term "fourth trimester" refers to the period immediately after birth, so it does not apply to pregnancy loss in the same context. Understanding these patterns of loss is crucial for healthcare providers supporting individuals during pregnancy.