Fetal Development
Learn more about fetal development, pregnancy, and when to test.
fetal development
Fetal development is the process of conception and growth inside a mother’s womb, also called gestation, the time between conception and birth.
Gestational age describes how far along a pregnancy is. It is measured in weeks from the first day of the last menstrual period (LMP) to the current date. A normal pregnancy typically ranges from 37 to 42 weeks.
When Pregnancy Begins and when to test
Because the exact day of conception is usually unknown, pregnancy is dated from the LMP, which is typically about two weeks before conception. This is why pregnancy can be described as lasting 37–42 weeks. If you think you may be pregnant, start with the following steps:
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Pregnancy testing
A pregnancy test picks up HCG (human chorionic gonadotropin) in the urine. HCG is present in the mother’s blood after conception, but it usually takes about 3–4 weeks from the first day of the LMP for HCG levels to be high enough for an at-home test to detect. -
Ultrasound confirmation
An ultrasound is the most accurate way to determine how far along you are and should be performed prior to an abortion. Due date calculators can not verify a viable pregnancy or the location of the pregnancy. -
Options consultation
If your pregnancy was unintended, contact us for a free consultation and the medical services you need to make an informed choice.
Pregnancy Trimesters
Pregnancy is often divided into trimesters based on symptoms and development:
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First Trimester: weeks 1–13
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The risk of miscarriage decreases after the first trimester
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Second Trimester: weeks 14–27
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Fetal viability (the ability for the baby to live outside the womb) occurs during the second trimester.
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Third Trimester: week 28 until delivery
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Early-term is considered 37 weeks and full t-term is 39 weeks or more.
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Some also refer to a fourth trimester after birth, the first three months of life, when a baby is especially dependent on its primary caregiver.
Stages of Fetal Development
Germinal Stage
This stage begins at conception when sperm fertilizes the egg in the fallopian tube, creating a zygote. The zygote travels to the uterus over about one week while rapidly dividing. It forms two structures: one becomes the fetus, and the other becomes the placenta, which supplies nutrients and oxygen throughout pregnancy.
Embryonic Stage
The embryonic stage lasts about five weeks, starting around week 3 of pregnancy. During this stage, key structures form, including:
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Major organs and body systems
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Neural tube (future brain and spine)
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Head, eyes, mouth, and limbs
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Heartbeat begins at 21-22 days after fertilization
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Arm and leg buds form around week 6
Cardiac activity can typically be detected via transvaginal ultrasound as early as 5½ to 6 weeks of gestation. By week 8, most organs and systems have taken shape, and many women begin experiencing morning sickness.
Fetal Stage
The fetal stage begins around week 9 and continues until birth. The fetus develops sex-specific organs around week 9, though this usually isn’t detectable by ultrasound until around 20 weeks.
Organs continue to grow and mature, and features like fingernails, eyelashes, and hair develop. Many mothers begin feeling fetal movement as early as week 16, though timing varies depending on how the pregnancy is carried and the fetus’s position in the uterus.
Schedule Your Appointment
Real Choices Women's Center offers free pregnancy confirmation services, including free pregnancy testing, ultrasound confirmation, information on abortion pills and procedures, pregnancy and parenting resources, and more. Contact us to schedule your free pregnancy test and get the information you need to make the best decision for you.