During those long nine months of pregnancy, it’s your favorite guessing game: What will your new baby look like? Will she be tall like one parent, or have the other's green eyes? Will she more closely resemble one parent than the other?

There’s no magical crystal ball that can predict your baby’s appearance exactly, but thanks to genetics, there are a few clues you can turn to while waiting for the big day.

What will my baby look like?

When it comes down to the color of your baby’s eyes, the texture of her hair or how tall she'll ultimately be, it all boils down to DNA: the instruction guide found in the nucleus of each of your cells that makes you you.

Genes are made up of DNA, and are comprised of two alleles. Your baby will inherit two alleles for each gene, one from each parent. But to make it a little more confusing than what you learned in your high school biology class, most traits that your baby will inherit are the result of multiple genes from both parents working together. That’s why there’s no foolproof way to guarantee your baby will look a certain way.

How genetics influence your baby’s hair color

If both you and your partner have brown or black hair: Your little one will likely have dark hair as well. Brown hair is dominant over blonde hair, so if your baby has two brown-haired alleles, or even one brown-haired allele and one blonde-haired allele, she’ll have brown hair. Likewise, if both you and your partner are blonde, your babies most likely will be blonde. This is because each parent also had two blonde-haired alleles.
If one parent is blonde and the other is brunette: It will be a bit of a guessing game. If the brown-haired parent has one brown allele and one blonde allele, there’s a 50-50 chance baby will be blonde. But if the parent has two brown alleles, then the brown will dominate and baby will be a brunette.
If one or both parents has red hair: Red hair is a little trickier. It’s a recessive allele, which means both parents have to have these alleles for their child to sport a carrot-top. If both you and your partner don’t have red hair but you both carry the recessive allele for red hair, you have a one in four chance of having a red-haired child.
If two brunette parents give birth to a blonde child: Both parents must have had one blonde allele, and one brunette one. As a result, they have a one in four chance of having a blonde child. One clue is to look back at old family photographs. If either you or your partner had a blonde grandparent, or even great-grandparent, there’s a chance you might have a blonde allele.

While this can provide a rough guide, keep in mind that there are several genes from each parent that determine hair color. It’s also impacted by other genes that control how much of a pigment called melanin you have in your hair. If you have a lot of one type of melanin, called eumelanin, you’ll have black or brown hair. If you have little eumelanin, you’ll have blonde hair.

Red-haired folks have a lot of another type of melanin known as pheomelanin. These genes help determine if you’re light or darker blonde, if you have brown or jet-black hair, and if you’re red-haired, whether you’re more of a strawberry blonde or a deep auburn.

How genetics influence your baby’s eye color

It’s hard to tell right away if your baby will have baby blues, browns or greens. Most white babies are born with blue or gray eyes, and Black, Indigenous and People of Color (BIPOC) infants are born with dark, usually brown, eyes. While BIPOC babies’ eyes will usually stay dark, the eye color of white babies may go through a number of changes due to pigmentation of the iris until baby’s first birthday.

But just like hair color, baby’s eye color is determined by several genes that control the production of the pigment melanin. These come in two types of alleles — one that’s for brown and blue eyes, and one that’s for green and blue. Brown is dominant over green and blue, while green is dominant over blue.

But two brown or brown and green-eyed parents can still occasionally have a blue-eyed child. This is because they could both have a recessive blue-eyed gene that they pass onto their baby.

How genetics influence your baby’s weight, height and build

You may give birth to a 22-inch, 10-pound boy, but that doesn’t mean he’ll be topping the growth charts for the rest of his life. There are many factors that impact your baby's growth in your belly, including your diet and how much weight you gained during your pregnancy. One way to get a rough guestimate of how tall your baby will ultimately be is to add your height and your partner’s height in inches, then add five inches for boys or subtract five inches for girls. Now divide by two. Add both Mom and Dad’s height in either inches or centimeters.

Weight is a little trickier. Research suggests that about 40 percent of a child’s weight predisposition is inherited from mom and dad (so 20 percent from each one). But it’s hard to tease out how much of that is truly genetics, and how much of that is environmental.

Do children look more like their mothers or fathers at birth?

You may have heard that a newborn looks more like her father than her mother. The evolutionary theory is that a dad is more likely to invest his time and resources if he’s certain that it’s his own offspring. If a baby pops out and appears to be his mini-me, it’s more reassurance that yes, he can confirm paternity.

But research shows that most infants resemble both parents equally, and in fact, some studies even suggest that newborns actually look more like their mothers in the first three days of life. One theory there is that evolution actually went the opposite way, because if a newborn represents Mom, Dad will claim and care for the baby even if it really isn’t his.

Why do some children look more like one parent?

If your baby grows up to look exactly like one parent, it doesn’t mean that she got more of one parent’s genes: each child gets the exact same number from both Mom and Dad.

The reason your child may favor you, say, instead of your partner (or vice versa) has to do with the versions of each gene she's inherited from each of you and the traits that combination gives them. Sometimes, a child doesn’t really look like either, and instead resembles an aunt or uncle or grandparent. That’s the mystery of genetics!

How does a newborn’s appearance change over time?

Once your newborn arrives, you may be surprised by just how much their appearance changes over the course of the first few days, weeks and months of life. Here’s a breakdown of some of your baby’s features that might be a surprise at first:

Large, pointy head. Babies arrive top-heavy — with their heads looking too large for their bodies. In fact, the newborn head has an average circumference of 13.8 inches and makes up about a quarter of the length of your baby's body (imagine that ratio on a grown-up!). If you’ve had a vaginal delivery — especially one in which you had to push for a long time — your baby's head may be pointy or cone-shaped, thanks to hours spent squeezing through the birth canal. Not to worry; cone heads round out in a few days or weeks. And no matter its shape, eventually your baby’s head will better match the size of her little body.
Hair. Newborn hair may be limited to a sprinkling of fuzz, or could be so full, it looks like it’s already due for a trim. It may lie flat or stand up straight in spikes.
Puffy eyes. The swelling around your baby’s eyes is also due, at least in part, to the rough road she took on that fantastic voyage into the world. Another contributing factor might be the antibiotic ointment placed in her eyes at birth. And here’s one more thought: Some experts speculate that this swelling serves as natural protection for newborns, whose eyes are being exposed to light for the first time. No matter what the cause, puffiness, too, is temporary — lasting just a few days. In the meantime, don’t worry that it might interfere with your baby’s ability to see you. Though she can’t yet distinguish one person from another, a newborn can make out blurry faces at birth — even through those swollen lids.
Bent ear. The bent ear probably also comes courtesy of the cozy but crowded conditions your baby experienced in her uterine home. As a fetus grows and becomes more snugly lodged in the mother’s amniotic sac, an ear that happens to get pushed forward may stay that way even after birth. Again, it’s only temporary — and it won’t interfere with your baby's ability to hear (or recognize) your voice.
Flattened nose. The pushed-in nose that may make your newborn look a bit like a baby boxer is also very likely the result of going a long round in your narrow birth canal. It, too, should return to its genetic blueprint.
Skin. Because a newborn’s skin is thin, it usually has a pale pinkish cast from the blood vessels just beneath it. Right after delivery, it’s most often covered with the remains of the vernix caseosa, a cheesy coating that protects fetuses during the time spent soaking in the amniotic fluid (the earlier a baby arrives, the more vernix is left on the skin). Babies born late may have skin that’s wrinkled or peeling (because they had little or no vernix left to protect it).
Genitals. Because of an infusion of female hormones from the placenta just before birth, many babies — both boys and girls — have swollen nipples and/or genitals. There may even be a milky discharge from the nipples and, in girls, a vaginal discharge (sometimes bloody).

Remember, your baby's appearance isn't set in stone. Most features develop and change throughout the first year and beyond. It's impossible to predict what your baby will look like as an adult, but here are some changes you can start to look for early on:

Weight gain. Most babies start to fill out by 3 weeks, looking less like scrawny chickens and more like softly rounded babies. In most cases, you can expect a breastfed baby to regain her birth weight in 2 weeks and then gain roughly 6 to 8 ounces a week for the next couple of months. Formula-fed babies usually gain weight faster in the beginning.
Eye color. Most white babies are born with dark blue or slate-colored eyes, while most BIPOC infants arrive with dark, usually brown, eyes. While BIPOC babies' eyes will usually stay dark, their shade can change slightly over time.
Skin color. If you or your partner are Black, your baby may be born with light skin — often a shade or two lighter than their skin color will end up. It could take weeks or months — or in some cases, a few years — before your little cutie shows her true colors. Looking for a sign of how pigmented she'll eventually be? Some parents swear that the ears will clue you in — check out the tops of your baby's tiny ears, and you'll notice that they're darker than the rest of your newborn's skin. There's a good chance her skin will wind up being close to that color. Babies of white parents might be paler, pinker or blotchier in the very beginning than they will be later in babyhood.

Be sure to capture those newborn features for the baby book or app, because they're all fleeting. Most disappear within the first few days, the rest within a few weeks, leaving nothing but darling dimpled cuteness in their place.