Fetal development in pregnancy week 20:fetus in fifth month This week you're carrying about 10.5 inches and 10.5 ounces of solid baby-miracle-goodness! Their little delicates bones continue to ossify and toughen while their itsy bitsy finger and toe pads are finishing up. Your little monkey now has teeth buds, although they’re hidden beneath the gum line. And finally! Their limbs have reached their relative proportions—no more alien baby! Their cute pink lips are more defined, and might be helping out in a bit of prenatal thumb-sucking. If you have a little boy, then their tiny testes are descending, though they have not yet passed the abdominal wall. What’s more, eyelashes and eyebrows are also visible. At this point, your little one really looks like a miniature baby—and we do mean miniature as your little swimmer currently weighs a mere eighth of their final birth weight. With half the pregnancy behind you, the most significant gains are yet to come!

Your amazing little baby is now around 10 inches in length! If this seems a bit shocking, you’ll be relieved to know they’ve not actually grown over 3 inches, but that their little legs are now straight enough to be measured. This is when doctors begin measuring fetal growth from head to toe, (no longer “crown to rump” or CR). Lanugo (little hairs) covers their whole body now, trapping that charming cheese-like vernix caseosa (see week 18) to the surface to the skin. This week your lil’ fetus will start on an appetizing diet of amniotic fluid which they are now capable of swallowing, digesting, and passing the fluid as far as their tiny “large” intestines. Fortunately for you, this nice little lump of baby-poop won’t be coming out while they’re still in your womb. Some time shortly after they’re born, this fun lump will become the first in a long line of baby poops. (What finally comes out— commonly known as “meconium” to the science world, will be black and sticky, and you’ll be very glad it happens only once!)

We have two more ounces! Your "getting bigger-n-better by the minute baby" is already up to 7 ounces and 6 inches! This is a big week for their baby skin. There are now two distinct layers—the epidermis (or the surface skin) and dermis. Currently, their skin is covered with a greasy, waxy, cheese-like substance, known as vernix caseosa. Sure, it sounds pretty nasty, but this mixture of fatty secretions covering your little swimmer from head to toe is the best way to protect their oh-so-thin skin from bruising and abrasions as well as chapping caused by amniotic fluid exposure (and your little one is swimming in that stuff!). Still don’t like the fact your little darling is currently slathered in fatty cream like a greased pig? Well, you know the birthing process? Where you have to push something the size of a watermelon out a hole the size of a grape? That adorable little greased piglet would have a lot harder time getting through the birth canal without the vernix caseosa. Fun fact for momma’s with baby girls: it’s a uterus within a uterus! Your little girl will have developed a uterus and vagina canal by the end of this week.

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Congratulations! Your amazing growing baby has been accepted into to the fetus-club, a very exclusive and exiting new stage in their prenatal development. Basically, this means the little sweet pea has graduated from swimming embryo creature to a recognizable human being! This week in particular, the irises of their little eyes can function, but (frustratingly for them?) their eyelids remain fused shut for a while yet. Their external ears are formed and their inner ears are now filled with fluid—so your little one is already developing their sense of balance. Your baby's little swimmer legs are still relatively, although other bodily developments are going forward at a nice pace: their kidney is actually functioning now, which means they’ve started urinating (this might seem charming now but wait till you have to start buying diapers!).

Woohoo! You've got one whole inch of baby inside of you! Your little embryo has finally reached the one-inch mark (30mm). And if it were possible to take a peek, you could actually see your tiny baby without a telescope! What’s more, your baby is finally starting to take on some very distinct human features. For starters, their little tail (really just the spinal cord) has disappeared completely. It’s nice to know your baby can no longer be mistaken for a sea creature! Additionally, both their toes and fingers are prominent with very little, if any, webbing. Upper and lower limbs all show recognizable joints (elbows and knees) and the lower limb bones are starting to ossify. But don’t expect your baby to resemble either parent quite yet. Right now, your baby’s head is disproportionately larger than the rest of their body--making up almost half of your little one’s height and weight!

Your baby is really beginning to develop more physical definition this week – their oversized head isn’t just large and oblong anymore, it’s actually a little bit pointy. The tiny receding tail bud is now starting to be overshadowed by the growth of their legs, which are now complete with knees and the beginnings of toes. Their eyes and ears are the most visible features on their head and their miniature bones are starting to harden throughout their body. You also have some variation on a boy or a girl at this point, although their genitals won’t be visible enough to determine which color cigars you’re going to buy until around the 16th week.

This is going to be a busy week for your amazing little embryo. Their brain is still growing remarkably fast; miniature hand plates are starting to develop and the early formations of what will be their fingers are already visible. Also, the lower limbs do not develop quite as fast, so they’re pretty much still flippers. Up until this point, your baby has been very curled up with the head and tail in close proximity, but this week their trunk and neck are beginning to grow and straighten as their tail recedes into its resting position in the back. Even though your little miracle is only 6 weeks old, they’re already capable of demonstrating reflex responses to touch!

The changes to your growing embryo are not quite as drastic this week as they've been in the last few weeks. Growth is now largely focused on their little head, which is starting to develop much more rapidly than the rest of their tiny body. This is because their amazing brain is undergoing some very crucial and rapid development in order to effectively regulate their heart rate, blood circulation, and other vital functions. As for the rest of their miniature body, what were simple limb buds last week are limb flippers this week and the tail is more expressed. Amazingly, within a mere five weeks your little miracle is already developing the rudimentary forms of their liver, pancreas, lungs, stomach and nasal pits while their little heart is already increasing its circulation. Your baby is now a whopping 4-6mm in length.

By the end of this week the round and pointy ends of your little pear-shaped baby will be slightly more exaggerated and their body will look more like that of a miniature manatee. Despite your baby not looking particularly human without any eyes, ears or mouth, the earliest developments of what will become the larynx, internal ear, and eye lens are already forming, although you’d have to be a trained expert to recognize them for what they’re going to be in the future. Likewise, tiny bumps are forming on your little embryo which will eventually be their cute little arms, elbows, fingers, legs, knees and toes. What’s more your little swimmer will have a teeny tiny tail by the end of this week-- but don’t worry, it’s just the end of their developing spinal cord! A microscopic photo would reveal what seems to be their vertebrae filling out the spine and tail. Although they aren’t bones yet, but rather, the “bone seeds” that will give rise to your baby's tiny vertebrae, ribs and sternum.