Congratulations! At 3 weeks pregnant, you’ve officially conceived and are in month 1 of your pregnancy — though it will be a few weeks until you can confirm the news with a pregnancy test.
This week, the tiny cluster of cells (soon to become your baby!) are rapidly growing. Meanwhile, surging hormone levels may trigger a heightened sense of smell, one of the earliest signs of pregnancy. If you’re 3 weeks pregnant, you're in month 1 of your pregnancy. Only 8 months to go! Still have questions? Here's some more information on how weeks, months and trimesters are broken down in pregnancy. You ovulated this week, and the moment you’ve been waiting for has finally arrived: You’ve conceived! Meaning your soon-to-be-fetus has started on its miraculous transformation from solitary cell to bouncing baby boy or girl. Once the winning sperm makes its way through the egg's outer layer, the single-cell fertilized egg — or zygote — immediately forms a barrier to keep other sperm out. But your zygote doesn't stay single for long. Within hours, it divides into two cells, then four, and so on, until the growing cluster comprises around 100 cells just a few days after that crucial first meeting between sperm and egg. Some will form the embryo, others the placenta, but for now, it’s still just one microscopic ball of cells that’s one-fifth of the size of the period at the end of this sentence. Watch your baby grow week-by-week with the What to Expect app! Tiny? Yes. But don't underestimate its potential. As it divides, the blastocyst, as it's now called (don't worry, you'll come up with a cuter name soon), travels this week from your fallopian tube to your uterus — a trip that takes about five or six days. Spoiler alert: Once it arrives during week 4, it will implant itself in the uterine wall and grow for the next nine months. In other words, congratulations! You've got yourself a baby-in-the-making, ready to begin the incredible journey that will end in your arms. So will your lone little cell miraculously become a girl or a boy? Though it will be months before you can find out for sure (if you decide to find out before delivery day), that remarkable determination has already been made, believe it or not. Ready for a crash course in biology? The fertilized egg contains 46 chromosomes — 23 from each biological parent. The mother always provides an X chromosome, but the father can provide either an X or a Y. If the sperm that fertilizes your egg carries an X, the XX zygote will be a girl. If the sperm is Y-bearing, your XY zygote will be a boy. For now, it will seem like nothing is happening on the outside — but only for the next couple of weeks. If your timing is right and you've had sex during ovulation, your egg has been fertilized by one lucky sperm and your body is gearing up to host the blastocyst (which will soon become your baby!) that's heading for the uterus, its home for the next nine months. So what's happening inside this week? Just after the egg is released, the follicle it came from gets a new tenant called the corpus luteum, a yellowish body of cells that occupies the space left by the egg. The corpus luteum starts to produce progesterone and some estrogen, enough of both pregnancy hormones to nourish and support the future baby until the placenta takes over in about 10 weeks. In the meantime, about a week after fertilization, the blastocyst (or soon-to-be embryo) implants itself in the uterine lining and the placenta starts to take shape. Within six to 12 days after snuggling into the uterus (around week 4 of pregnancy), the cells of the newly developing placenta begin making human chorionic gonadotropin (hCG). HCG surges during the first trimester before dipping in the second, tells your ovaries to stop releasing eggs and triggers the production of more progesterone and estrogen — which keep the lining of the uterus from shedding and support the growth of the placenta. As you'll later see, all these hormones play an important role throughout your pregnancy and cause a whole host of body changes, plus symptoms like morning sickness (yay?). Traces of hCG can be picked up in urine and blood — which explains why home pregnancy tests have you pee on a stick and your OB/GYN runs a blood screening at your first appointment — but you probably won’t get a positive result on a pregnancy test for another week or two. Do scents suddenly seem stronger to you than ever? It could be a sign that you're pregnant! A heightened sense of smell is a very real side effect of pregnancy caused by hormones such as estrogen and hCG, which magnify every little fragrance (the good, the bad and the ugly) wafting in the air around you. Whether it's the food your neighborhood restaurant is cooking up, the garbage on the street corner or your partner's cologne or perfume, your keener-than-ever nose might be picking it up. The downside of your new superpower? It can ramp up your morning sickness even more. If that's the case, steer clear of the kitchen and local eateries as much as possible, make friends with the microwave (which tends to cause less of a stink) and open the windows. You can also try washing clothes more often and switching to unscented toiletries. And don't be shy about asking your partner, family and friends to clean up after a workout, go easy on the perfume and brush their teeth after chowing down on that garlicky pasta or onion-loaded burger. Toss some berries in your cereal. Adding vitamin C-laden foods to iron-rich fare can increase your body’s absorption of iron, which helps support your baby’s developing blood supply and ups your odds of a healthy pregnancy. You can find vitamin C in fruits and vegetables like oranges, grapefruit, kiwis, mangoes, strawberries, melons, bell peppers, tomatoes and asparagus. Iron can be found in soy, beef, poultry and dried fruit. Now that you’re in baby-making mode, it’s time to trade your cocktail for a mocktail. Heavy drinking not only messes with your menstrual cycle, making it harder to get pregnant, but it can also increase the risk of birth defects. It’s best to abstain from alcohol entirely, but don’t stress if you unwittingly indulged in a few drinks before finding out you were pregnant. A glass or two — especially so early on in your pregnancy — is unlikely to cause serious harm. You’ve tracked your cycle, pinpointed your ovulation window, and gotten busy between the sheets — now, you have to wait … and wait … and wait. There’s a window between ovulation and the day your period comes called the two-week wait, and for many women, those 14 days or so can be fraught with anxiety. Take advantage of the time to binge-watch a TV show or tackle your to-do list (you may not have nearly as much time once baby is on board). Or, if you’re feeling particularly stressed, do some walking, reading or journaling (you can use our My Journal app tool to jot down notes about how you’re feeling) to relax. More twins and triplets are being born in the U.S. than ever before. But the chance of getting pregnant with twins is still small — about 3 in 100. Still, your odds of seeing double go up if twins run in your family (though only on the mom’s side) or you’ve given birth to twins before. Undergoing fertility treatments also increases your chances of having multiples; they’re responsible for about a third of twin births and three-fourths of triplet, quadruplet and other higher-multiple births, according to one study. In the past, you had to miss your period before you took a home pregnancy test (HPT) — then wait a couple of hours before learning the results. These days, you can find out you're expecting much earlier, faster and with better accuracy than ever before (though accuracy will, of course, get better the closer you are to that missed period). So theoretically you could take one this early if you wanted to! Still, it can take a week or more after you miss your period before you produce enough of the pregnancy hormone human chorionic gonadotropin (hCG) to be detected on a test. If you're late and negative, retest in a few days. You’re drinking for two these days — so keep the fluids coming, to the tune of about eight to 12 8-ounce glasses a day. Water helps your body absorb essential nutrients and shuttle them into the blood cells, which are then transported to the placenta. Try to space out your fluid intake throughout the day as opposed to gulping down a bottle of H2O all in one sitting (drinking liquids all at once can leave you feeling uncomfortably full). Drink water, sparkling or flavored waters, fruits and vegetable juices (or diluted juice), or weak decaffeinated non-herbal tea. You’ll know you’re drinking enough fluids if your urine is pale or colorless. If you have baby’s estimated due date, you can also figure out the most likely conception date: Just subtract 266 days from when you expect baby will arrive — or let our Pregnancy Due Date Calculator do the math for you. It’s not always an exact science, though: Sperm can live in your body for several days before joining with an egg — and an egg can wait around for 24 hours before fertilization occurs.Your Baby at Week 3
At a Glance
3 weeks pregnant is how many months?
How big is my baby at 3 weeks?
Implantation
Boy or girl?
Your Body at Week 3
The corpus luteum and pregnancy hormones
Pregnancy and sense of smell
Pregnancy Symptoms Week 3
Tips for You This Week
Reviewed September 3, 2024 From the What to Expect editorial team and Heidi Murkoff, author of What to Expect When You're Expecting. What to Expect follows strict reporting guidelines and uses only credible sources, such as peer-reviewed studies, academic research institutions and highly respected health organizations. Learn how we keep our content accurate and up-to-date by reading our medical review and editorial policy.
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