Fetal development is the process by which a human is conceived and develops in a mother’s womb. This process can also be referred to as gestation, which is the period of time between conception and birth when a baby grows inside the mother.

The term gestational age refers to how far along a pregnancy has progressed. Gestational age is measured in weeks, from the first day of the woman’s last menstrual cycle to the current date. A normal pregnancy can range from 38 to 42 weeks.Stages of Fetal Development

There are three stages of fetal development, the germinal stage, embryonic stage, and the fetal stage.

Germinal stage

The germinal stage begins at conception when a sperm and egg join in the fallopian tube. The sperm fertilizes the egg, creating a zygote. The zygote travels to the uterus in the span of about one week. During this time frame, the zygote is already rapidly dividing multiple times into two structures, one which develops into a fetus and another structure that develops into the placenta. Throughout a pregnancy, the placenta will provide nutrients and oxygen to the developing fetus.

Embryonic stage

The embryonic stage of pregnancy lasts for about five weeks, beginning approximately around the third week of pregnancy. During the embryonic stage, the following features form:


    • Structures and organs

    • Neural tube that later develops into the spine and brain

    • Head, eyes, mouth and limbs

    • Heart begins to develop and pulse around week six.

    • Buds that will become arms and legs form around week six.

By the eighth week of pregnancy, most of the embryo’s organs and systems have taken shape. For a lot of women, this is the point in pregnancy where morning sickness begins.

Fetal stage

The fetal stage of pregnancy begins around week nine and lasts throughout the remainder of the pregnancy. Around week nine, the fetus develops the organs distinguishing its biological sex, though this will not be detectable with an ultrasound until approximately twenty weeks into pregnancy.

Major organs and body systems continue to develop and grow for the fetus. Fingernails, eyelashes, and hair grow. The movements of the fetus’ limbs are typically detectable, meaning the mother will be able to feel them, as early as the sixteenth week of pregnancy.

This can vary as different women carry their pregnancies differently, some higher, some lower, some more toward their backs, and some more prominently outward. Depending on where the fetus is located in the uterus, the fetus’ movements might be detected earlier or later.

When Pregnancy Begins

Since the precise day of conception is typically indeterminable, a pregnancy technically begins the day of your last menstrual period. This is usually two weeks before conception even occurs and accounts for why a healthy pregnancy can last anywhere from 37 to 42 weeks long.

How Conception Works

A woman’s body undergoes a natural reproductive cycle every single month. There are four phases in a woman’s menstrual cycle–menstruation, follicular phase, ovulation, and the luteal phase. There are two possible outcomes each month for this reproductive cycle:


    1. Menstrual Period

    1. Pregnancy

During the ovulation phase of a woman’s menstrual cycle, an egg is released from the ovaries and travels down the fallopian tube to the uterus. Ovulation typically occurs two weeks before menstruation, when a woman’s period begins. As soon as the egg is released, it survives for 24 hours.

Since sperm are viable for up to five days, this means a woman is fertile and can get pregnant five days leading up to the day of ovulation and the day of ovulation.

Pregnancy Trimesters

Pregnancy is often referred to in terms of trimesters. A pregnancy trimester is a term used to categorize the various phases of pregnancy in terms of pregnancy symptoms. There are three trimesters throughout the course of a full-term pregnancy:


    • First Trimester: 1-12 weeks of pregnancy

    • Second Trimester: 14-27 weeks of pregnancy

    • Third Trimester: Week 29 until the baby is delivered.

It is growing more common to refer to an additional fourth trimester after the baby is delivered. This fourth trimester spans the first three months of an infant’s life outside the womb, when it is necessary for the baby to be especially attached and dependent on its primary caregiver, mainly its mother.

Fetal “Viability”

The term “viability” refers to the likelihood a baby has of surviving after being born. This term is somewhat arbitrary, and there is a lot of debate about when an infant is considered “viable”. When medical practitioners use this term, they typically are referring to the likelihood of a fetus surviving outside the womb with little to no medical intervention.

Fetuses are typically considered viable at week 26 of pregnancy. According to research conducted by the Liverpool Women’s NHS Foundation Trust, 80% of babies born at 26 weeks survive.

What “Full Term” Means

Near the end of a pregnancy, healthcare practitioners will use a variety of terms to describe the likelihood of complications at birth. These terms include:


    • Early Term – A baby born between 37 and 38 weeks is considered an early term baby.

    • Full Term – A baby born between 39 and 40 weeks.

    • Late-Term – A baby born the 41st week

    • Post-Term – A baby born 42 weeks or later.

If the baby is born before 37 weeks, it may be considered premature and may be susceptible to certain health complications depending on how developed they are. An infant can be born as early as 23 weeks and live with the support of intensive medical care. The earlier an infant is born, the more the likelihood of medical and health complications increases.

When to Take a Pregnancy Test

A woman is typically fertile five days before ovulation and the day of ovulation. The hormone human chorionic gonadotropin (HCG) is present in the mother’s blood from the moment of conception. However, it will take about three to four weeks from the first day of a woman’s last period for there to be enough HCG in the mother’s blood for an at-home pregnancy test to detect it.

This is why it is advisable to not take a pregnancy test until the week of when your period is supposed to start again or after a missed period.

Schedule Your Appointment

Inspira Resource Center offers free pregnancy confirmation services, including free pregnancy tests and limited ultrasound. Inspira Resource Center also offers free educational resources on all of your reproductive options, including abortion, adoption, and parenting. Contact Inspira Resource Center today to schedule your free pregnancy test and be empowered with the information you need to make the best decision for you.