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Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman.[4] A multiple pregnancy involves more than one offspring, such as with twins.[13] Pregnancy usually occurs by sexual intercourse, but can occur through assisted reproductive technology procedures.[6] A pregnancy may end in a live birth, a spontaneous miscarriage, an induced abortion, or a stillbirth. Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP).[4][5] This is just over nine months – (gestational age) where each month averages 31 days.[4][5] When using fertilization age it is about 38 weeks.[5] An embryo is the developing offspring during the first eight weeks following fertilization, (ten weeks gestational age) after which, the term fetus is used until birth.[5] Signs and symptoms of early pregnancy may include missed periods, tender breasts, morning sickness (nausea and vomiting), hunger, and frequent urination.[1] Pregnancy may be confirmed with a pregnancy test.[7]
Pregnancy is divided into three trimesters, each lasting for approximately 3 months.[4] The first trimester includes conception, which is when the sperm fertilizes the egg.[4] The fertilized egg then travels down the fallopian tube and attaches to the inside of the uterus, where it begins to form the embryo and placenta.[4] During the first trimester, the possibility of miscarriage (natural death of embryo or fetus) is at its highest.[2] Around the middle of the second trimester, movement of the fetus may be felt.[4] At 28 weeks, more than 90% of babies can survive outside of the uterus if provided with high-quality medical care.[4]
Prenatal care improves pregnancy outcomes.[9] Prenatal care may include taking extra folic acid, avoiding drugs, tobacco smoking, and alcohol, taking regular exercise, having blood tests, and regular physical examinations.[9] Complications of pregnancy may include disorders of high blood pressure, gestational diabetes, iron-deficiency anemia, and severe nausea and vomiting.[3] In the ideal childbirth labor begins on its own when a woman is "at term".[14] Babies born before 37 weeks are "preterm" and at higher risk of health problems such as cerebral palsy.[4] Babies born between weeks 37 and 39 are considered "early term" while those born between weeks 39 and 41 are considered "full term".[4] Babies born between weeks 41 and 42 weeks are considered "late term" while after 42-week they are considered "post term".[4] Delivery before 39 weeks by labor induction or caesarean section is not recommended unless required for other medical reasons.[15]
About 213 million pregnancies occurred in 2012, of which, 190 million (89%) were in the developing world and 23 million (11%) were in the developed world.[11] The number of pregnancies in women aged between 15 and 44 is 133 per 1,000 women.[11] About 10% to 15% of recognized pregnancies end in miscarriage.[2] In 2016, complications of pregnancy resulted in 230,600 maternal deaths, down from 377,000 deaths in 1990.[12] Common causes include bleeding, infections, hypertensive diseases of pregnancy, obstructed labor, miscarriage, abortion, or ectopic pregnancy.[12] Globally, 44% of pregnancies are unplanned.[16] Over half (56%) of unplanned pregnancies are aborted.[16] Among unintended pregnancies in the United States, 60% of the women used birth control to some extent during the month pregnancy occurred.[17]
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