Pregnancy is the time period from conception to delivery during which a baby develops in the mother's womb. For due date calculations and milestone assessments, pregnancy is counted from the first day of the last menstrual period, which occurs about two weeks before conception.
For many people, a missed menstrual period is the first sign of pregnancy[1]. Pregnancy lasts approximately 40 weeks. Full term means 39 weeks through 40 weeks and 6 days; early term means 37 weeks through 38 weeks and 6 days. Birth before 37 weeks is preterm[2].
The timeline of a pregnancy is separated into three trimesters, each lasting approximately 12 to 14 weeks. During the earliest stages, the developing baby changes from a fertilized egg into a ball of cells known as an embryo. At the end of eight weeks, after major organs have begun to form, the developing baby is considered a fetus[1].
Key takeaways
- Pregnancy tests detect the hormone hCG, and testing too early can produce a false negative result.
- Pregnancy is divided into three trimesters with changing fetal development and physical symptoms.
- Labor progresses through cervical dilation, birth, and delivery of the placenta.
Types of Pregnancy Tests
Pregnancy can be detected through blood tests or urine tests. Pregnancy tests detect human chorionic gonadotropin (hCG), a hormone produced by the placenta. Blood tests can detect lower levels than urine tests, and testing too early can produce a false negative. Waiting to test until 1 to 2 weeks after the first missed menstrual period provides a more reliable result[3].
Urine-based pregnancy tests simply detect whether hCG is present. Because they tend to provide rapid, accurate results, these are typically used to diagnose a pregnancy both through at-home tests and in a doctor's office.
Blood tests can either detect the presence of hCG or the actual amount of hCG present in the blood sample. Quantitative hCG tests can help clinicians monitor early pregnancy and investigate possible miscarriage or ectopic pregnancy; they do not confirm these conditions or a multiple pregnancy on their own[3].
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Integrative mental health care
View profileStages of Labor
The start of labor marks the beginning of the birthing process and the end of pregnancy. Labor may progress quickly and be over in less than an hour or may continue for days before the baby is born. There are three stages of labor:
Early and Active Labor
Early labor begins with contractions, which are typically irregular at first. A clear or pink discharge may appear as the mucus plug sealing the cervix is released.
As contractions become more regular and the cervix begins to dilate, early labor shifts into active labor. As the cervix dilates to approximately 10 centimeters in diameter and contractions become closer together, this signals the final part of active labor, called transition.
Birth
After about 15 to 60 minutes of transition, the birth process begins, and the baby emerges into the world headfirst. The process of birth can take anywhere from a few minutes to a few hours.
Delivery of the Placenta
After the birth of the baby, the parent's body releases the placenta. This stage usually lasts 5 to 30 minutes and involves further contractions[4].
The First Trimester
The first trimester of pregnancy includes everything from the first day of the last menstrual period to the 12th week of pregnancy. During the first trimester, the fertilized egg develops into an embryo, which implants into the uterine wall.
The amniotic sac, placenta, and umbilical cord form during this trimester. By the end of the first trimester, the fetus is approximately .5 to 1 ounce and 3 to 4 inches long[1].
During this stage of pregnancy, the pregnant individual may experience symptoms of pregnancy, including nausea, mood swings, swollen breast tissue, and fatigue. The developing fetus is also particularly susceptible to external influences that can hamper development, such as exposure to alcohol, drugs, medications, environmental toxins, infectious diseases, and radiation.
The Second Trimester
The second trimester is the period from the 13th week to the 28th week of pregnancy. During this trimester, early symptoms such as nausea and fatigue often begin to ease[1].
During the second trimester, visible signs of pregnancy start to develop, including growth of the belly and breasts. New symptoms may emerge, including leg cramps, Braxton Hicks contractions, increased vaginal discharge, and dental sensitivity. Many pregnant people experience reduced fatigue and increased excitement about the upcoming birth, while some individuals may develop anxiety related to birth and parenting[5].
The Third Trimester
The third trimester of pregnancy includes everything from the 29th week of pregnancy through birth, which usually occurs at around 40 weeks. As the due date approaches, most babies settle into a head-down position. The lungs and other organs continue maturing during the final weeks of pregnancy. At birth, the fetus usually weighs between 6 and 9 pounds and measures around 19 to 21 inches[1].
The growing fetus puts pressure on other organs in the mother's body during the last trimester. This often results in an increased need to urinate, more frequent heartburn, difficulty taking deep breaths and frequent backaches.
Fluid retention can cause swelling, particularly in the hands, face, and ankles. The discomfort of late pregnancy can take a toll on mental and emotional health, but this is usually temporary, since these symptoms typically go away after birth.
Some women experience a condition called postnatal depression after birth that makes it difficult to care for the newborn. Depression that occurs during pregnancy or after childbirth is called perinatal depression; depression after birth is also called postpartum or postnatal depression.
Symptoms of perinatal or postpartum depression include feelings of sadness, hopelessness, anxiety, irritability, and fatigue to the point of being unable to carry out self-care tasks. Treatment may be necessary during pregnancy or after birth; persistent or severe symptoms should be discussed with a healthcare professional[6].
References
- Office on Women’s Health. (2025, September 26). Stages of pregnancy. U.S. Department of Health and Human Services. Office on Women’s Health. Accessed October 10 2026.
- Eunice Kennedy Shriver National Institute of Child Health and Human Development. (2022, June 2). Know Your Terms: Moms-to-be. National Institutes of Health. National Institute of Child Health and Human Development. Accessed October 10 2026.
- National Library of Medicine. (n.d.). Pregnancy Test. MedlinePlus. MedlinePlus. Accessed October 10 2026.
- Office on Women’s Health. (n.d.). Labor and birth. U.S. Department of Health and Human Services. Office on Women’s Health. Accessed October 10 2026.
- Mayo Clinic Staff. (2025, February 7). 2nd trimester pregnancy: What to expect. Mayo Clinic. Mayo Clinic. Accessed October 10 2026.
- National Institute of Mental Health. (n.d.). Perinatal Depression. National Institutes of Health. National Institute of Mental Health. Accessed October 10 2026.
