How Many Weeks is the First Trimester?

Expect Change During the First Three Months of Pregnancy

Having a baby is one of life’s greatest experiences, a journey that lasts approximately 42 weeks. The beginning of the pregnancy—also known as the first trimester—lasts 12 weeks or about three months. Every week, your baby changes and grows, developing into the new little person you can’t wait to welcome into your family.

In the Beginning

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How Soon Do Pregnancy Symptoms Start?

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To determine a woman’s due date, pregnancy is measured from the first day of her last menstrual period, meaning that the first trimester encompasses the period between week one and week 12 of the pregnancy. Most women usually don’t learn they're pregnant until weeks four through seven, so they could be halfway through the first trimester before they know they're expecting. In most cases, women learn they're pregnant when a period is missed. They may, however, experience other symptoms such as tender or swollen breasts, nausea, increased urination, fatigue, food aversions, heartburn and constipation.

Head to the Doctor

While today’s home pregnancy tests are extremely accurate, it’s important to find a doctor and begin your prenatal care once you suspect you're pregnant. This includes a health assessment, checking for risk factors and determining the baby’s gestational age, which helps determine your due date. You’ll also discuss concerns or fears and what you're currently experiencing along with what’s to come, diet considerations and prenatal vitamins. Going forward, you can expect to have follow-up appointments every four weeks; the frequency will increase the closer you get to your due date.

Be Emotional

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Emotional Symptoms During Third Trimester of Pregnancy

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As with all life changes, expecting a baby is accompanied by emotions: excitement, joy and elation, as well as fear, nervousness and anxiety. This is normal. Crying unexpectedly is also common. To deal with these emotions, talk with your partner, your loved ones and even your doctor. They can provide much-needed emotional support and encouragement.

Sharing the News

Some couples can’t wait to share the news that they're expecting while others hold off, waiting to get through the first trimester to ensure the pregnancy is progressing as it should. When to tell your family and friends you're pregnant is entirely up to you; don’t feel pressured or rushed to share the news right away. For many women, especially first-time moms-to-be, a baby bump starts to develop between 12 and 16 weeks. Women who have been pregnant before may start to show sooner. Be warned though: Women who have experienced pregnancy may spot the signs that you're pregnant. Be prepared to confirm or deny if questioned.