Nonpregnant and Pregnant Women with 5 and 9 Month Fetuses lateral view

A woman's body undergoes enormous changes during pregnancy. The heart and kidneys must work harder due to increased blood volume: cardiac output increases 30-50% during pregnancy. Heart rate increases to 80-90 beats per minute. The enlarged uterus which reaches the lower edge of the rib cage by 36 weeks compresses the bladder and intestines making it necessary to urinate frequently and possibly causing constipation. The spine curves more to balance the weight of the growing uterus. The breasts enlarge and begin to produce colostrum in the final weeks of pregnancy.

Pregnancy, also known as gravidity or gestation, is the time during which one or more offspring develops inside a woman. A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy can occur by sexual intercourse or assisted reproductive technology. It usually last around 40 weeks (10 lunar months) from the last menstrual period (LMP) and ends in childbirth. This is about 38 weeks after conception. An embryo is the developing offspring during the first 8 weeks following conception after which the term fetus is used until birth. Symptom of early pregnancy may include a missed periods, tender breasts, nausea and vomiting, hunger, and frequent urination. Pregnancy may be confirmed with a pregnancy test.

Pregnancy is typically divided into three trimesters. The first trimester is from week one to twelve and includes conception. Conception is followed by the fertilized egg traveling down the fallopian tube and attaching to the inside of the uterus where it begins to form the fetus and placenta. The first trimester carries the highest risk of miscarriage (natural death of embryo or fetus). The second trimester is from week 13 to 28. Around the middle of the second trimester movement of the fetus may be felt. At 28 weeks more than 90% of babies can survive outside of the uterus if provided high quality medical care. The third trimester is from 29 weeks to 40 weeks.

Prenatal care improves pregnancy outcomes. This may include taking extra folic acid, avoiding drugs and alcohol, regular exercise, blood tests, and regular physical examinations. Complications of pregnancy may include high blood pressure of pregnancy, gestational diabetes, iron deficiency anemia, and severe nausea and vomiting among others. Term pregnancy is 37 weeks to 41 weeks, with early term being 37 and 38 weeks, full term 39 and 40 weeks, and late term 41 weeks. After 41 weeks it is known as post term. Babies born before 37 weeks are preterm and are at higher risk of health problems such as cerebral palsy. It is recommended that delivery not be artificially started with either labor induction or caesarean section before 39 weeks unless required for other medical reasons.

About 213 million pregnancies occurred in 2012 of which 190 million were in the developing world and 23 million were in the developed world. This is about 133 pregnancies per 1,000 women between the ages of 15 and 44. About 10% to 15% of recognized pregnancies end in miscarriage. In 2013 complications of pregnancy resulted in 293,000 deaths down from 377,000 deaths in 1990. Common causes include maternal bleeding, complications of abortion, high blood pressure of pregnancy, maternal sepsis, and obstructed labor. Globally 40% of pregnancies are unplanned. Half of unplanned pregnancies are aborted. Among unintended pregnancies in the United States, 60% of the women used birth control to some extent during the month pregnancy occurred.

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