The first trimester consists of the first 14 weeks of the 40-week pregnancy. During this time, a woman may experience various emotions due to the hormonal changes in her body, and she may experience “morning sickness” at any time during the day or night.
During the first trimester, nearly all of the fetus’ internal organs form. The fetus is approximately the size of a fist and can even begin to move a little.
During the second trimester, weeks 15 through 27, a woman may experience symptoms of heartburn and indigestion. The baby’s growth in the abdominal area becomes noticeable, and stretch marks may develop as the skin of the abdomen expands. The developing fetus grows very rapidly during the second trimester, and the fetus’ arms and legs become well developed and strong. The expectant mother may begin to feel the baby moving inside. Although the fetus is almost fully formed, the lungs need to develop further while the fetus puts on more fat and weight.
During the third trimester, weeks 28 through 40, the baby continues to grow and the lungs develop further. It can be difficult for a woman at this stage to find a comfortable position either awake or asleep.
The baby’s growing body within the uterus pushes the abdominal organs up under the diaphragm and compresses the bladder and colon. Near the end of the 40-week cycle, the baby drops down into the pelvic cavity, which is nature’s way of saying, “It’s time to give birth”.
Review Date: 11/12/2021
Reviewed By: John D. Jacobson, MD, Department of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
Cell division
1:42
Cesarean section
3:47
Conception - general
1:46
Conception - pregnancy
3:20
Conception of identical twins
0:33
Early labor
0:52
Egg cell production
3:54
Egg production
4:02
Fetal ear development
1:13
Formation of twins
3:44
Human face formation
1:57
Intracytoplasmic sperm injection
0:49
Kids - How big is the baby?
1:15
Kids - How does the baby co...
0:42
Kids - Is it a girl or boy?
1:14
Kids - Umbilical cord
1:19
Kids - Where do babies come...
0:50
Ovulation
0:38
Placenta delivery
0:57
Placenta formation
Preeclampsia
0:18
Pregnancy
1:26
Sperm production
2:28
Sperm release pathway
1:53
The role of amniotic fluid
1:45
Twin-to-twin transfusion sy...
1:11
Ultrasound
2:55
Vaginal delivery
0:53
Vasectomy
0:32
Breast engorgement
2:48
C-section
2:14
Endometriosis
2:38
Hysterectomy
2:24
Infant formulas
2:37
Newborn jaundice
2:16
NICU consultants and suppor...
3:13
Pregnancy care
3:18
Storing breast milk
2:07
24-week fetus
Abnormal discharge from the...
Abnormal menstrual periods
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Amniocentesis
Amniotic fluid
Anatomy of a normal placenta
Antibodies
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Bananas and nausea
Before and after vasectomy
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Blood cells
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Bulging fontanelles
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Early weeks of pregnancy
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Female breast
Female reproductive anatomy
Female reproductive anatomy...
Female urinary tract
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Fetus at 10 weeks
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Fetus at 16 weeks
Fetus at 26 to 30 weeks
Fetus at 3.5 weeks
Fetus at 30 to 32 weeks
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First trimester of pregnancy
Folic acid
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Gestational ages
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Large fontanelles
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Macrosomia
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Morning sickness
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Newborn head molding
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Normal female breast anatomy
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Placenta
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Polyhydramnios
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Side sectional view of fema...
Single palmar crease
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Stein-Leventhal syndrome
Sunken fontanelles (superio...
The cervical cap
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Ultrasound, color - normal ...
Ultrasound, normal fetus - ...
Ultrasound, normal fetus - face
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Ultrasound, normal placenta...
Ultrasound, normal relaxed ...
Umbilical cord healing
Uterus
Vaginal bleeding during pre...
Vaginal ring
Well baby visits
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CPR - infant - series
Exchange transfusion - series
Rh incompatibility - series