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S e x - While the  s e x  is determined from the time of fertilization, it is not visible until around 16 to 18 weeks. The external  s e x  organs are fully formed around 20 weeks.

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Lanugo -

Starting at 16 weeks, a fetus will grow hair all over its body, known as lanugo. They shed the lanugo before birth, which is ingested in amniotic fluid intake, and expelled in the first poop.

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Language learning - Researchers have found that language learning begins in utero.

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Language learning - In their mother's belly, they are learning to distinguish between the sounds of their native language. Once born, they will be quicker to respond and more interested in the language they were surrounded with in the womb.

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Sleep - Babies sleep 90-95% of their time in the womb, according to website Parents. Some of these hours are spent in deep REM sleep, where scientists believe they may be dreaming.

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Vernix caseosa - Babies are born covered in a cream-cheese-like film, known as the vernix caseosa. The purpose of the coating is to protect the growing baby's skin from the amniotic fluid.

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H a i r y baby - A Johns Hopkins University study found that the more hair a baby has, the more heartburn a mother will experience.

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Senses - Babies can smell and taste the food their mother eats as it is reflected in the amniotic fluid.

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Senses - The development of smell also serves to prepare the baby to recognize the scent of their mother and her breast milk.

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Taste - Babies can develop food preferences while in utero, based on what their mother is eating. Some babies have been seen licking the placenta after their mother has eaten one of their favorite foods, according to website BabyGaga.

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Hearing - The study of fetal movement, respiration rate, and heartbeat has shown that babies will respond to music in the womb and even remember it after birth, according to Livestrong.

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Hearing - At 24 weeks, babies' ears are fully formed and they can hear the sounds that their mother's body makes, including digestion, breathing, and talking.

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Hiccups - Hiccuping begins in the first trimester. The hiccups are a reflex and meant to prepare a baby for drinking and breathing.

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Facial movement - According to an article on Live Science, fetuses demonstrate constant facial movement while in the womb. The complexity of movement increases over time and eventually resembles recognizable facial expressions.

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Babies play -

Babies are very active while in utero. They have even been known to play—they touch their bodies and walls of the uterus and have even been seen tugging on and playing with the umbilical cord.

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Play - Not only does a developing fetus respond to familiar voices and sounds, it can also imitate touch, such as when someone pokes the mother's belly and it "pokes" back in the same place.

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Crying - Babies begin crying and screaming at 28 weeks gestation. They may often react to loud noises by crying.

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Self-soothe - In ultrasound images, it is common to catch babies sucking their thumb and touching their mouth. This is not only a method of self-soothing, it also prepares the baby for anticipating touch associated with feeding.

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Smiling - Digital imaging has caught babies smiling while in the womb. It is thought that smiling may be a sign of contentment.

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Male erections - Male babies can start getting erections immediately after birth, and sometimes even in the womb.

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Amniotic fluid -

The amniotic fluid is essentially urine. The baby is constantly drinking the fluid and peeing it out in an endless cycle.

The amount of fluid can also be used as an indicator for baby's health. If there is not enough fluid, the baby's kidneys may not be developing correctly and too much fluid can indicate difficulty with swallowing.

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First poop - Throughout the entire gestational period, the baby is creating their first poop, called meconium. Made of cells, amniotic fluid, and hair, this poop has a tar-like consistency and is incredibly stinky.

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Light -

Babies have been seen flinching away from bright light when shown directly towards the uterus. They have also been witnessed opening and closing their eyes as if blinking, which is thought to prepare them for the world outside of the womb.

See also: Historical figures who were nepo babies

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