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Baby Development at 20 Weeks

By Norma DeVault ; Updated June 13, 2017

You’re halfway there. Twenty weeks into pregnancy or 18 weeks after conception marks the midpoint of a normal full-term pregnancy and you may feel the baby’s first movements, known as quickening, at this point, according to Growth and development continue on a dramatic course. Within a very few weeks, the baby could survive outside the womb with the intensive care technology available to preterm babies today. The best opportunity for a baby to survive and thrive, though, is to continue developing in mother’s womb until the appointed time.


To avoid confusion, take note of whether a timeline refers to weeks of pregnancy or weeks of gestation. Because of the way due dates are calculated from the beginning of the last period, the time allotted to a pregnancy usually includes two weeks before conception occurs. So a pregnancy lasting 40 weeks includes a normal 38 weeks of gestation, according to

Doctors often calculate due dates this way because most women can recall the day their last period started and this is more accurate than other means of estimating a date of possible conception. Unfortunately, different sources use different methods of dividing the 40 weeks into months and trimesters so that can be an additional source of confusion to expectant mothers.

New Developments

As a woman completes her 20th week of pregnancy or 18th week of gestation, her baby’s heartbeat may be audible with an ordinary stethoscope. He may suck his thumb and occasionally have the hiccups. Her hair, eyelashes and eyebrows are present, according to John Santrock in the text “Life Span Development.” The baby is more active and may show a preference for a specific position in the womb. Critical immunities transfer from mother to baby to protect him from viruses to which the mother has previously been exposed.

Continued Developments

Specialized areas of the brain are developing nerve cells for the five senses, including taste, smell, hearing, seeing and touch. Nerve cells grow larger and make complex connections. The baby may startle in response to loud sounds that he can now hear. She can hear noises outside the womb and after birth may find familiar sounds calming, according to A baby girl’s uterus is developing now and her ovaries at birth will contain about a million eggs.

Baby’s Length And Weight

At 20 weeks of pregnancy or 18 weeks gestation, the baby is about 6 1/3 inches long, measured from the crown of his head to his rump. He likely weighs at least 11 oz., according to

Maternal Developments

Besides weight gain, many other physical and biochemical changes are also occurring in the mother to support the pregnancy. Blood volume increases by 50 percent. Blood pressure may decrease in the second trimester. Other maternal responses to pregnancy include increased retention of salt and water, cardiac output increases and hyperventilation occurs, according to Arthur Vander, James Sherman and Dorothy Luciano in the text “Human Physiology.”

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