What is pregnancy?

Pregnancy refers to the period when a fetus (or more than one fetus) develops inside your uterus. It most often happens after sexual intercourse, but it can also occur with the help of assisted reproductive technologies (ART). The most common way to confirm pregnancy is with a home pregnancy test, although a blood test can also confirm it. Some of the earliest signs of pregnancy include a missed period, nausea and fatigue.

Most pregnancies end with the birth of a live baby, either through vaginal delivery or a C section. Some pregnancies end in miscarriage, abortion or stillbirth.

How does pregnancy happen?
Pregnancy is a complex process that involves several steps, but it begins with an egg and a sperm.

Eggs are stored in the ovaries. During each menstrual cycle, one ovary releases an egg. The egg slowly travels through the fallopian tube, where it waits for sperm. This process is called ovulation and lasts about 12 to 24 hours.

Sperm is produced in the testicles. During ejaculation, millions of sperm are released from the penis. During sexual intercourse, sperm travels through the vagina and up into the fallopian tubes.

For pregnancy to occur, a sperm and an egg must meet and join together. This is called conception. The sperm fertilizes the egg in a process known as fertilization. The fertilized egg travels down the fallopian tube and begins dividing into many cells, forming a structure called a blastocyst. After about three days, the blastocyst reaches the uterus. It then attaches to the uterine wall in a process called implantation and becomes an embryo. After implantation, the placenta begins to form. The embryo later develops into a fetus, which is the term used until birth.

Once implantation occurs, the body releases pregnancy hormones that prevent menstruation and support the development of the fetus.

Assisted reproductive technology ART
With ART, the process is similar, but some steps happen outside the body. The egg and sperm are still essential, but a healthcare provider helps them come together more easily.

Intrauterine insemination IUI
A healthcare provider places sperm directly into the uterus using a thin tube called a catheter. This is done during ovulation. Some women take fertility medications to increase the chances of ovulation.

In vitro fertilization IVF
A healthcare provider combines the egg and sperm in a laboratory to create an embryo. The embryo is then placed into the uterus. Medications may be used during IVF to improve the chances of a successful pregnancy.

How many weeks is pregnancy?
Pregnancy lasts about 40 weeks or 280 days. The length is calculated from the first day of the last menstrual period, even though ovulation usually happens about two weeks later. This means that by the time a pregnancy test is positive, the pregnancy is already considered about four weeks along.

A healthcare provider confirms the due date using ultrasound and medical evaluation.

If pregnancy occurs through IVF, the total length is still 40 weeks, but the calculation may differ slightly because fertilization happens outside the body.

How do you calculate your due date?
You can estimate your due date using this method. Write down the first day of your last menstrual period. Add seven days. Subtract three months. Add one year.

Your healthcare provider will confirm or adjust your due date during prenatal visits. Only about five percent of babies are born exactly on the estimated due date.

What does gestational age mean?
Gestational age refers to how far along the pregnancy is. It is calculated from the first day of the last menstrual period and is expressed in weeks and days, for example 22 weeks and 3 days. It describes the duration of the pregnancy, not the exact age of the fetus.

What are the trimesters of pregnancy?
Pregnancy is divided into three trimesters. Each trimester lasts about three months or 13 weeks.

What can you expect in each trimester?
Each trimester brings different changes and symptoms. The uterus grows significantly, starting about the size of a lemon and growing to the size of a watermelon by the end of pregnancy.

First trimester
The first trimester lasts until week 13. Common symptoms include fatigue, morning sickness, breast tenderness, food cravings or food aversions, heartburn, constipation, mood changes and headaches. Healthcare providers usually recommend prenatal vitamins and advise avoiding alcohol, tobacco, drugs and certain unsafe foods.

Second trimester
The second trimester lasts from week 13 to week 28. Many women feel better during this period. The fetus begins to move, and weight gain becomes noticeable. Other symptoms may include body aches, skin darkening and changes in breast appearance.

Third trimester
The third trimester lasts from week 29 to week 40. The fetus grows rapidly and gains weight. Common symptoms include shortness of breath, back pain, frequent urination, sleep discomfort, breast leakage of colostrum and signs that the body is preparing for labor.

What does full term pregnancy mean?
A full term pregnancy lasts between 39 weeks and 40 weeks and 6 days. Babies born during this time have the highest chance of being healthy. Early term is between 37 and 38 weeks. Late term is week 41. Post term is after 42 weeks.

What kind of care do you need during pregnancy?
Prenatal care is very important for both the mother and the fetus. Healthcare providers monitor health, track fetal growth and check for possible complications.

During prenatal visits, providers may perform physical exams, measure blood pressure and weight, listen to the fetal heartbeat, perform ultrasounds, order blood tests and screen for infections or genetic conditions. They also provide guidance and answer questions.

Prenatal appointment schedule
Appointments usually occur every four weeks until week 28, every two weeks until week 36 and every week until delivery.

How much weight should you gain during pregnancy?
Weight gain varies for each person, but most healthcare providers recommend gaining about 11 to 16 kilograms during pregnancy.