Week 4 of Pregnancy
This is a milestone week, many people discover they’re pregnant around Week 4, often after a missed period. Behind the scenes, big things are happening. Your baby is now a blastocyst implanting in your uterine lining, and your body is starting to support new life.
Baby’s Size
Your baby is about the size of a sesame seed.
Baby’s Development at 4 weeks
Implantation is Complete
The fertilized egg (now called a blastocyst) finishes implanting into your uterine lining, starting the official journey of pregnancy.
Placenta & Amniotic Sac Begin Forming
Two key support systems start developing: the placenta (to deliver nutrients) and the amniotic sac (to cushion your baby).
Tiny but mighty, your baby is about 0.04 inches long, and too small to be seen without a microscope.
Baby Is the Size of a Sesame Seed
Foundations for Major Organs Begin
The inner cell mass will become your baby, starting the early groundwork for the brain, spine, and heart.
Pregnancy symptoms during week 4
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Pregnancy hormones plus your body's increasing blood volume may equal a near-constant need to pee. During pregnancy, running to the bathroom much more than you'd like is a fact of life. It's important to stay hydrated, but you may want to cut back on fluids late in the day so you don't have to get up to pee as frequently at night.
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Breast tenderness can be one of the first signs of pregnancy. It usually starts around 4 to 6 weeks and lasts through the first trimester. You may notice your breasts growing or your nipples darkening. Some women also see prominent blue or purple veins develop on their breasts in early pregnancy.
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For many women, exhaustion is one of the early signs of pregnancy. Pregnancy fatigue affects almost all expecting moms in the first trimester, likely due to a dramatic rise in progesterone.
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Morning sickness – also called nausea and vomiting of pregnancy – affects different expecting moms at different times (and some not at all). It usually starts around week 5 or 6 of pregnancy.
For some women, that telltale queasy feeling is one of the first giveaways that they're pregnant. There are safe ways to get relief from morning sickness, including changes to your diet and lifestyle, natural remedies, and medication. Be sure to talk to your provider if you're suffering.
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Does the smell of your coworker's lunch suddenly make your stomach churn? Food aversions often start around now. Most expecting moms experience them, thanks to changing hormones and a heightened sense of smell.
Some of the most common aversions include meat, coffee, eggs, dairy, and foods with a lot of spices or fat. To cope, try eating bland or cold foods. If cooking makes you sick, ask a loved one to cook for you or get takeout.
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About 1 in 4 women experience spotting or light bleeding during the first trimester. It's often nothing, but sometimes it's a sign of miscarriage or ectopic pregnancy.
Call your doctor or midwife just in case. And if you're actively bleeding or you have severe pain and can't reach your provider, head to the emergency department right away.
Pregnancy checklist at 4 weeks pregnant
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Once you get a positive pregnancy test, call your doctor or midwife and make your first prenatal appointment. Many healthcare providers will schedule your first visit for when you're about 8 weeks pregnant. Some will see you sooner, particularly if you have a medical condition, have had problems with a pregnancy in the past, or are having symptoms such as vaginal bleeding, abdominal pain, or severe nausea and vomiting.
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Always check with your provider before you take any kind of medicine during pregnancy – prescription medicine or even an over-the-counter (OTC) product. If you take medication currently, ask your provider whether it's a safe medicine for pregnancy. Your doctor or midwife can help you find a good alternative if it isn't.
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If you're plagued by gas, bloating, or an uncomfortable sensation in your gut, try eating smaller meals throughout the day. Eat slowly and chew your food well, don't drink too much water during meals, and avoid carbonated beverages, gum, and the artificial sweetener sorbitol. Exercise, like walking or prenatal yoga, can also provide relief.
4 Weeks Pregnant Belly
Though you just found out you're pregnant, you may already feel the button on your pants digging into your belly. That's due to bloating, which can make your clothes uncomfortable even this early in your pregnancy journey.
It will be a few months before you need maternity clothes, but until then you'll probably appreciate things that are loose-fitting at the waist. You’ll be glad you have these items as your body starts to change more:
leggings
joggers
sweats
maxi dresses
There may be a period where your regular clothes don't fit, but you're not ready to wear maternity clothes yet either , that's normal. This in-between phase is a good time to shop your closet with an eye for soft knits, athleisure, loose-fitting blouses, oversize cardigans, and roomy dresses. These items can also be helpful if you aren't ready to announce your pregnancy yet, and want to keep well-meaning-but-curious friends and colleagues at bay.
Tips & Resources
Start by taking prenatal vitamins and making time for rest and hydration. Your body is already hard at work. Our Preparing for Your New Arrival Guide offers a simple overview to help you organize your thoughts and plan your next steps with ease.
If you have a partner or support person, involve them early, pregnancy is a shared journey. Our Partner Support Guide outlines how your loved one can help reduce stress, stay connected, and be your best support from the very beginning.
It’s also a good time to begin tracking symptoms and building awareness of what’s normal in early pregnancy. Looking ahead? Our Third Trimester Pregnancy Tip Sheet gives you a sneak peek of what’s to come, so you can understand why what you do now matters later.
Feeling unsure about your care provider or birth plan? Start exploring your options now, and consider joining our 7-Week Prenatal Group Series for expert guidance and a supportive community. You can also book a Private 1-on-1 Prenatal Class tailored to your needs and schedule.