Here's everything you need to know about abortion later in pregnancy according to doctors, not politicians, including how often it occurs and why it's necessary.

Abortion was legalized in the United States in 1973 out of the Supreme Court case Roe v. Wade. Since then, abortion has been politically debated, and one way politics has entered abortion policy is within its terminology.

You've likely seen some abortions referred to as 'late-term abortion'. However, 'late-term abortion' is not a recognized medical term. According to the American College of Obstetrics and Gynecology, "the term 'late-term abortion' has no medical definition and is not used in a clinical setting or to describe the delivery of abortion care later in pregnancy."

Adds Gillian Dean, M.D., MPH, senior director of medical services at Planned Parenthood Federation of America: "People who oppose abortion have made up terms—such as 'partial-birth abortion' and 'late-term abortion'—to further stigmatize ending a pregnancy. To be clear: There is no such thing as an abortion up until birth, and 'late-term abortion' is not a term used by reputable health care providers."

Still, we often hear these terms in the news—and you may have even mistakenly used them yourself. We chatted with experts to clear up the confusion.

RELATED: Termination of Pregnancy for Medical Reasons

What's the correct term for 'late-term abortion'?

"Generally people mean abortion performed after 12 weeks or 3 months, but it's better to specify exactly which period of gestation one is talking about," says Daniel Grossman, M.D., director of Advancing New Standards in Reproductive Health (ANSIRH) at Bixby Center for Global Reproductive Health at the University of California, San Francisco.

Keeping abortion terminology by gestation period is the proper way to define it. "We talk about care as pregnancy progresses in weeks from a person's last menstrual period, or in trimesters (1st: 0-13 weeks, 2nd: 14-26 weeks, 3rd: 27-40 weeks)," says Chelsea Souder, MPH, director of Clinical Services and Communications Manager at AbortionClinics.org.

What about 'partial-birth abortion'?

This term originated from the Partial-Birth Abortion Ban Act of 2003. However, it's not a defined procedure recognized by leading medical groups, including American College of Gynecology (ACOG), according to the Guttmacher Institute.

"'Partial-birth abortion' refers to a procedure known as dilation and extraction, or D&X, which involves attempting to remove the fetus intact through the cervix," explains Dr. Grossman. "The procedure is no longer legal unless medication is used to stop the fetal heartbeat first."

When do most women have abortions?

Since 1973, when abortion was legalized nationally, around 11 percent of abortions have occurred at or after 13 weeks gestation. According to the Guttmacher Institute, here is when women have abortions percentage-wise:

Earlier than 8 weeks: 66%

66% 9-10 weeks: 14.5%

14.5% 11-12 weeks: 8.3%

8.3% 13-15 weeks: 6.2%

6.2% 16-20 weeks: 3.8%

3.8% After 21 weeks: 1.3%

When is second or third trimester abortion necessary?

While most abortions occur before 8 weeks, second or third trimester abortions are also options women may have. These are the most common reasons an abortion may occur during the second or third trimester:

Fetal anomalies

"The medical reasons for an abortion in the second trimester include a diagnosis of fetal malformation or genetic anomaly," says Dr. Grossman. These include: anencephaly, the absence of the brain and cranium above the base of the skull, or limb-body wall complex, when the organs develop outside of the body cavity, according to the ACOG.

Mother's medical complications

"Medical complications are the development of a condition in the pregnant woman that necessitates delivery," says Dr. Grossman. "Some examples of these conditions include severe preeclampsia, or high blood pressure of pregnancy, or bleeding from a placenta previa, when the placenta covers the cervical opening of the uterus."

Other medical complications include: premature rupture of membranes and infection, placental abruption, and placenta accreta, which may risk extensive blood loss, stroke, and septic shock that could lead to maternal death, according to the ACOG.

Less access to care

Second and third trimester abortions may also be more common in places with more strict abortion laws.

"Our research in Texas found that the restrictive laws there, which led to the closure of about half of the abortion clinics, were associated with an increase in second trimester abortion," says Dr. Grossman. "The obstacles that women face accessing care ends up pushing them later in pregnancy before they can obtain a wanted abortion."

Adds Souder, "These restrictions have forced many clinics to close, in turn creating waiting lists, sometimes two to three weeks out. Unnecessary waiting periods, gestational bans, and lack of providers in rural areas force people in some states to travel hundreds of miles to get care. Thirty-five states currently ban state Medicaid from covering abortion care, which affects the most marginalized people."

"Nearly 99 percent of abortions happen before a person is 21 weeks pregnant, and those that happen later almost all happen before 24 weeks. In rare and very complex circumstances, abortions may be necessary later on in a pregnancy—such as when there are severe fetal anomalies or serious risks to the pregnant person's health," says Dr. Dean. "These unexpected and potentially life-threatening complications are why it's critical that patients and doctors have the option of abortion later in pregnancy. Ultimately, the decision to end a pregnancy depends on a person's unique circumstances, and should be between them and their doctors."

What is the procedure like for second trimester abortion?

In general, there are two options: "One option involves the use of medications to essentially induce labor to deliver the pregnancy. This may take a day or longer," says Dr. Grossman. "The second option is dilation and evacuation, or D&E, which involves opening the cervix and using instruments to remove the pregnancy. This usually takes less than 30 minutes and can be done under sedation or anesthesia."

Twenty states currently ban the D&E procedure, according to the Guttmacher Institute.

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