The loss of a fetus before the 20th week of pregnancy is referred to as miscarriage, also known as spontaneous abortion or early pregnancy loss. Miscarriage rates might vary greatly amongst women due to various factors. This post discusses miscarriage statistics depending on age, weeks of pregnancy, chances of miscarriage during assisted reproduction, and statistics of recurrent miscarriages.
How Many Pregnancies End In Miscarriage?
Spontaneous abortion or pregnancy loss may occur for approximately half of the pregnancies before the woman knows she was pregnant. About 10 to 15% of known pregnancies end in miscarriage (1). Around 15% of miscarriages may happen in the second trimester, that is, between 13 and 19 weeks of pregnancy (2). Second-trimester miscarriages are often called late miscarriages. A pregnancy loss that happens after 20 weeks of gestation is called a stillbirth, and it is not included in miscarriage statistics. It is possible to have healthy pregnancies after a miscarriage too, and this is a natural process. You should try to understand it and not be emotionally affected by it. Medical termination of pregnancy (MTP) or medical abortions and self-induced abortions or self-induced miscarriages are not included in the rates mentioned above.
When Does Miscarriage Happen?
Most miscarriages tend to occur in the first trimester, that is, within the first 13 weeks, and this period accounts for around 80-85 % of all cases (3) (4). Among these, most incidences of miscarriages happen during the first seven weeks of pregnancy. The risk of miscarriage can be higher or lower in each stage of pregnancy, depending on multiple maternal and fetal factors. Early pregnancy losses can be due to genetic factors, such as chromosomal abnormalities in the fetus. Early pregnancy loss factors are mostly beyond the control of women.
What Are The Miscarriage Rates By Week?
The miscarriage rate may vary depending on multiple factors among women. The relative risk of miscarriage by the week of pregnancy can be the following (5) (6).
3-4 weeks: This is the time when implantation occurs after the last menstruation, and pregnancy tests become positive. 50–75% of pregnancy loss happens before a positive pregnancy test, that is, before the fourth week. This is called chemical pregnancy and often indicated by other pregnancy and miscarriage symptoms.
5th week: The miscarriage rate can be around 21.3 %, according to a 2013 study. However, there can be a higher or lower risk of pregnancy loss depending on the maternal and fetal causes.
6–7 weeks: The rate of miscarriage during this week is about 5% since it is a point when the fetal heartbeat is obtained.
8–13 weeks: The miscarriage rate drops in this period to around 2–4%.
14–20 weeks: There is only a 1% chance of miscarriage during these weeks.
What Are The Miscarriage Rates By Age?
The miscarriage rate usually increases with age. The declining quality of ovum (egg) with increasing age could be one of the major causes of a higher incidence of pregnancy loss with advanced maternal age. The ovum has genetic problems in the form of chromosomal abnormalities. The frequency of pregnancy loss for women at different ages is the following (3). Note: Paternal age over 35 years could also increase the risk of spontaneous abortion (7). Research demonstrates that the pregnancy loss risk among women increases with maternal age, irrespective of reproductive history. Typically, it is lowest in women aged 19 years and below and highest in those aged 45 and above (16).
Rates of miscarriage as women grow older
The above-mentioned risk of miscarriage is purely based on maternal age. However, several other risk factors, such as chronic illnesses, lifestyle, and hormonal changes, could influence the miscarriage rate.
Risk Of Miscarriage And IVF
There is a chance of early pregnancy loss in 10-25% of the IVF-ET cycle (in vitro fertilization and embryo transfer) (8). The pregnancy loss after an IVF procedure may affect you emotionally, physically, and financially since the pregnancy is not continued and often another IVF cycle is required. Miscarriage is an indication that the embryo was implanted into the uterus. Biochemical pregnancy (positive pregnancy test) is also considered as a positive indicator for pregnancy. Chromosomal anomalies could be a significant cause of spontaneous clinical abortions.
Recurrent Miscarriage Rate
Recurrent miscarriage, habitual abortion, or repeated pregnancy loss (RPL) is a loss of three consecutive pregnancies before 20 weeks from the last menstruation. About 1–2% of women may experience repeated miscarriages, and it can leave many couples physically and mentally drained (9). Repeated miscarriage can be due to genetic factors, autoimmune conditions, infections, anatomical problems, or other unknown reasons. You may seek expert help to identify the cause and treatment to have a healthy pregnancy in the future.
Chance Of Miscarriage After Fetal Heartbeat
The miscarriage rate declines at the point after the fetal heartbeat is detected on the ultrasound (1). Some studies suggest a 10% drop in the miscarriage rate once the baby’s heartbeat is detectable (10). Many women may not be aware of fetal heartbeat until the first prenatal ultrasound scan by the 11th or 12th week. However, those who had fertility treatment may undergo scans earlier to accurately detect the risk of miscarriage based on the fetal heartbeat.
When Does The Risk Of Miscarriage Drop?
The pregnancy loss or miscarriage rate by week reduces when the pregnancy progresses. The risk of miscarriage may start to decline as early as when fetal heartbeats are detectable, which is around the 7th week of pregnancy. However, a significant decline in the rate of miscarriage occurs after 12 weeks of gestation. The drop in the miscarriage rate can also depend on other risk factors. For instance, chromosomal abnormalities could cause early pregnancy loss, while maternal factors like fibroids could result in late miscarriages.
What Should You Do If You Experience A Pregnancy Loss?
You may consult a gynecologist or any other doctor if you experience a miscarriage. They can give you the required treatment or help you identify the reason for pregnancy loss and resolve it. The pregnancy tissue may not be expelled entirely during miscarriages in some cases. You may require an ultrasound examination to confirm the complete miscarriage. If any tissues are left in the uterus, then your doctor may initiate treatment to remove these tissues and avoid complications. Miscarriage rates by week may vary depending upon several maternal and fetal factors. Nonetheless, if you have excessive bleeding and signs of infection during pregnancy, you must seek immediate medical attention. Your doctor may advise preventive measures, such as administering Rh immunoglobulin, if you have an Rh-negative blood type to reduce the risk of complications in your subsequent pregnancies.
