At 25 weeks, a woman is over the half-way mark of her pregnancy, which lasts 40 weeks. The fetus has gone from a sperm and an egg to a cluster of dividing cells, and now resembles a human. As the pregnancy progresses from this week, the baby's development is more focused on refining existing characteristics and gaining body fat.
Viewing the baby at 25 weeks via an ultrasound can reveal a nearly perfect baby. All external body parts have formed and the gender can be identified if the baby is in a position that allows the technician to view the genitalia. MedlinePlus points out that all parts of the eyes have developed along with eyebrows and eyelashes. During the weeks prior, the baby grew a fine hair called lanugo all over her body. Real hair on the head has also started forming in most babies, notes MayoClinic.com.
Around 25 weeks, a baby is about 13-inches long, states the American Pregnancy Association. This length is calculated by taking a crown to rump measurement, or measuring from the top of the head to the base of the bottom near the tailbone, while viewing the infant on ultrasound. The weight of the baby can vary, but most weigh more than 1 1/3 lbs.
At 25 weeks, a baby can open and close her eyelids and can exhibit the startle reflex. The startle reflex can be seen when a baby is surprised by a sound or motion; her hands fly out and open wide. The baby is still very active and a mother is likely to feel movement whenever the baby is awake. Fetal kick counts may be a part of the mother's day at this stage or in the coming weeks, according to the American Pregnancy Association. To perform fetal kick counts, a mother times how long it takes a baby to make 10 movements, or she may count the movements the baby performs within an hour, depending on what her caregiver prefers. Measuring movement like this increases the likelihood that a mother will catch a problem with her baby early. Tracking measurement also reassures the mother that the baby is doing fine.
Around the 25th week and going forward, the infant's brain develops rapidly, according to MedlinePlus. The body is storing fat. In future ultrasounds, the baby will appear to be filling out more. His hands and feet will be refined to the point that fingerprints and footprints will form. Inside his lungs, air sacs are growing, which will be put to use in the coming months during practice breathing. WhattoExpect.com explains that the baby's nostrils are plugged prior to the 25th week, but at this point, they will open and the vocal chords will continue refining in preparation for use at birth.
Many nervous system functions begin or improve around the 25th week and going forward. MedlinePlus explains that at this stage, the nervous system can control some bodily functions. This includes being receptive to touch. The baby's nerve-endings are not fully developed yet, but she may respond inside the womb when the mother's stomach is touched. The baby has been swallowing for several weeks, states MayoClinic.com, and if the baby is female, her ovaries are in place and are equipped with a lifetime supply of eggs.