From the Guidelines
Miscarriage risk varies significantly across pregnancy trimesters, with the highest risk occurring in the first trimester, approximately 10-20% of known pregnancies end in miscarriage, with about 80% of these occurring in the first trimester (before 13 weeks) 1.
Risk of Miscarriage by Trimester
The risk of miscarriage is highest in the first trimester and decreases substantially in the second and third trimesters.
- First trimester (before 13 weeks): 10-20% of known pregnancies end in miscarriage, with about 80% of these occurring in this period.
- Second trimester (13-26 weeks): the risk decreases to about 1-5%.
- Third trimester (after 26 weeks): pregnancy loss is rare and is typically referred to as stillbirth rather than miscarriage, with rates of approximately 0.3-0.5% 1.
Factors Influencing Miscarriage Risk
Several factors can influence the risk of miscarriage, including:
- Advanced maternal age (particularly over 35)
- Previous miscarriages
- Certain chronic conditions like uncontrolled diabetes or thyroid disease
- Smoking
- Alcohol consumption
- Some medications
- Genetic abnormalities in the embryo, which account for about 50% of early miscarriages 1.
Maintaining a Healthy Pregnancy
While no specific medication regimen prevents miscarriage in most cases, maintaining a healthy lifestyle, taking prenatal vitamins with folic acid, managing chronic conditions, and attending regular prenatal appointments can support a healthy pregnancy 1. Most miscarriages are not preventable and do not reflect anything the pregnant person did wrong. It is essential to prioritize prenatal care and maintain a healthy lifestyle to minimize the risk of miscarriage and support a healthy pregnancy 1.
From the Research
Risk of Spontaneous Abortion in Pregnancy
The risk of spontaneous abortion, also known as miscarriage, varies across the three trimesters of pregnancy.
- The first trimester is the most common time for miscarriages to occur, with approximately 10-15% of pregnancies resulting in spontaneous first trimester miscarriage 2, 3.
- The majority of these early losses are caused by chromosomal abnormalities, including aneuploidies and structural alterations 4, 2, 5.
- Around 50% or more of first trimester miscarriages are attributed to chromosomal instability, which can result in partial trisomies and monosomies 4.
- The risk of miscarriage decreases as the pregnancy progresses, but it can still occur in the second and third trimesters.
- Recurrent miscarriage, defined as two or more consecutive pregnancy losses, is a complex condition with multiple possible causes, including genetic factors, uterine anomalies, and hormonal disorders 6.
Trimester-Specific Risks
- First Trimester: The risk of miscarriage is highest during this period, with most losses occurring due to chromosomal abnormalities 4, 2, 5.
- Second Trimester: The risk of miscarriage decreases, but it can still occur due to various factors such as uterine anomalies, cervical insufficiency, and placental abruption.
- Third Trimester: The risk of miscarriage is relatively low, but it can still occur due to factors such as placental abruption, fetal growth restriction, and premature rupture of membranes.
Genetic Factors
- Genetic factors play a significant role in recurrent miscarriage, with approximately 70% of miscarriage conceptions revealing some chromosome abnormality 6.
- Specific gene mutations have been implicated in sporadic and recurrent miscarriages, and emerging data suggest that genetic factors contribute to conditions associated with recurrent pregnancy loss 5.