A pregnancy lasts for about 40 weeks. The weeks are grouped into three trimesters, first trimester, second trimester and third trimester. The first trimester is the time in between fertilization of the egg by the sperm (conception) and week 12 of a pregnancy.
A woman’s body goes through many changes during the first 12 weeks of a pregnancy. Women often start to have concerns over:
- what to eat
- which types of prenatal tests they should consider
- how much weight they might gain
- how they can make sure their baby stays healthy
Understanding a pregnancy week by week can help you make informed decisions and prepare for the big changes that lie ahead.
Baby’s growth during the first trimester
During the first trimester alone your baby changes from a single fertilized cell (a zygote), to the embryo that implants itself in your uterine wall, to a peach-sized bundle of growing limbs and body systems. Organs take shape, and baby starts to move. Here are a few of the big highlights happening in this exciting time:
- Baby’s bones: By about week 6, baby starts to sprout arms, legs, hands and feet — and fingers and toes around week 10.
- Hair and nails: Skin begins forming between weeks 5 and 8, with hair follicles and nail beds forming around week 11.
- Digestive system: By about week 8, baby’s intestines will begin forming, and your baby will have already gone through two sets of kidneys (with the third and final set on its way!).
- Sense of touch: Your baby will have touch receptors on his face (mostly lips and nose) around week 8. By week 12, he’ll have receptors on his genitals, palms and the soles of his feet.
- Eyesight: Optic nerves (which pass info from the eyes to the brain and back) and lenses begin to form by week 4, with the retina beginning to form around week 8.
- Heart: By week 5, the tube that will become your baby’s heart begins to beat spontaneously. It will become stronger and more regular — and you’ll be able to hear it! — around week 9 or 10 (though sometimes later, depending on your baby’s position in your uterus).
- Brain: By about week 8 of pregnancy, your baby’s brain will be wiggling his developing limbs.
- Sense of taste: Your baby will have developed taste buds that connect to his brain by about week 8 — but he’ll need taste pores before he can taste the surrounding amniotic fluid (which, by the way, tastes like your most recent meal).
A lot happens for you in the first trimester, too. A couple of the most common early symptoms of pregnancy you may experience:
- Morning sickness: Unfortunately it doesn’t just strike in the morning — and it typically starts up by about week 6 of pregnancy. Ginger tea or drops might help, as can small but frequent meals. If it’s severe, you might want to consider talking to your doctor about medications to treat the symptoms of pregnancy-related nausea.
- Tender breasts: So tender, so tingly, and so big! You might be wondering where your old boobs went by about week 6.
- Mood swings: You may (or may not) feel up, then down, then up again by week 7. If you have a history of depression or think it might be more serious, talk to your doctor about getting screened for prenatal depression.
As your pregnancy progresses this trimester, you may experience plenty of other pregnancy symptoms — heartburn, constipation, metallic taste, food aversions and headaches.
First trimester to-dos
- Start a prenatal vitamin. If you haven’t already, start taking a prenatal vitamin immediately — doing so in the first trimester has been shown to greatly reduce the risk of neural tube defects (like spina bifida).
- Choose your practitioner. There are a number of different practitioners you can choose for your pregnancy, from OB-GYN to midwife to family physician. So take time to consider your options and pick the right practitioner for your needs.
- Book your first ob-gyn visit. Your doctor will review your medical history and perform a thorough physical exam. You’ll likely undergo a battery of tests, including a Pap smear, urinalysis and blood work to determine your blood type and Rh status, hCG levels and the presence of any infections. You’ll likely have an initial ultrasound to confirm a heartbeat, date your pregnancy and be sure things are progressing as they should. You might also be screened for genetic illnesses or diabetes, depending on your family history. While your practitioner will ask lots of questions, be prepared to ask plenty of your own: Now’s the time to inquire about the safety of any medications you’re currently taking, help for quitting smoking or anything else that’s on your mind.
- Consider genetic tests. You’ll likely have a nuchal translucency screening (between weeks 10 and 13 of pregnancy) to look for Down syndrome and congenital heart defects; based on your risks, your practitioner may also recommend NIPT around week 9 (a noninvasive blood screening that looks for chromosomal abnormalities) and/or invasive but more definitive prenatal tests (chorionic villus sampling or amniocentesis).
- Look into health insurance options. The cost of pregnancy varies based on a number of factors (and it’s a whole lot more expensive if you don’t have health insurance). So now’s the time to sign up for a plan or review the terms of your policy, focusing on your premiums and co-insurance to keep your overall costs as low as possible.
- Make a budget. Growing your family is an excellent — and necessary — time to reevaluate your monthly expenses. So know the cost of having a baby, then set up your monthly budget.
- Eat right. Now’s the time to cut down on caffeine, as well as to learn which foods to avoid and which to feature in your pregnancy diet so you can stock your kitchen accordingly.
- Carve out time for fitness. There are lots of benefits of exercise during pregnancy for you and baby — which can be good motivation to get your 30 minutes of physical activity most days of the week.
- Have sex, if you feel like it. It’s fun and safe for baby — plus it has benefits for both of you.
- Start thinking about baby names. If you don’t have a baby name in mind, it’s never too early to start tossing around ideas.
- Plan to announce your pregnancy. Think about how and when you want to tell your friends and family the good news, and if and when you’ll announce on social media. Most women wait until the end of the first trimester to do so, when the risk of miscarriage is lower. And if you’re employed, start thinking about when to tell your boss your pregnant and what to say; do your research in advance to understand your company’s maternity leave policies.
What to avoid
These things should be avoided during the first trimester:
- strenuous exercise or strength training that could cause an injury to your stomach
- caffeine (no more than one cup of coffee or tea per day)
- illegal drugs
- raw fish or smoked seafood (no sushi)
- shark, swordfish, mackerel, or white snapper fish (they have high levels of mercury)
- raw sprouts
- cat litter, which can carry a parasitic disease called toxoplasmosis
- unpasteurized milk or other dairy products
- deli meats or hot dogs
Find out more about the first trimester
Categories: Pregnancy week by week