A–Z Glossary

Neural tube

The neural tube is an early embryonic structure that develops into the brain and spinal cord.

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Key milestones during each month of pregnancy

Key milestones during each month of pregnancy

How pregnancy months relate to weeks and trimesters Pregnancy is commonly divided into three trimesters: weeks 1 to 12, weeks 13 to 27, and weeks 28 to birth. Month-by-month descriptions are approximate because calendar months do not align perfectly with gestational weeks. Clinically, your care team will usually communicate in weeks and days, such as […]

Baby development month by month during pregnancy

Baby development month by month during pregnancy

Understanding pregnancy months and gestational age Pregnancy is usually dated from the first day of the last menstrual period, not from the exact day of conception. Because ovulation and fertilization typically occur about two weeks later in a 28-day cycle, a person who is “6 weeks pregnant” may have an embryo that has been developing […]

How pregnancy changes month by month

How pregnancy changes month by month

Understanding pregnancy timing: weeks, trimesters, and months Pregnancy is usually dated from the first day of the last menstrual period, even though conception typically occurs about two weeks later in a 28-day cycle. A full-term pregnancy is commonly described as about 40 weeks. Clinicians often use trimesters because they align with major developmental and medical […]

Pregnancy month-by-month overview

Pregnancy month-by-month overview

How pregnancy months are counted Pregnancy is medically dated in weeks, not calendar months, because fetal development changes quickly and because months vary in length. A 40-week pregnancy is divided into the first trimester through week 12, the second trimester from weeks 13 to 27, and the third trimester from week 28 until birth. Month-by-month […]

Month 2 of pregnancy: body changes, baby growth, and early symptoms

Month 2 of pregnancy: body changes, baby growth, and early symptoms

Where month 2 fits in pregnancy dating Pregnancy is typically dated from the first day of the last menstrual period, not from conception. That means by the time a home pregnancy test is positive, many people are already around 4 to 5 weeks pregnant. Month 2 generally covers weeks 5, 6, 7, and 8, though […]

Month 1 of pregnancy: symptoms, embryo development, and what to expect

Month 1 of pregnancy: symptoms, embryo development, and what to expect

How month 1 is counted Pregnancy is usually measured by gestational age, which starts on the first day of the last menstrual period. This convention is useful because the exact day of fertilization is often unknown. In a typical 28-day menstrual cycle, ovulation and conception occur around week 2 of gestational age, although cycle length […]

Baby size and fetal development milestones by trimester

Baby size and fetal development milestones by trimester

Understanding pregnancy dating and fetal size measurements Pregnancy is usually dated from the first day of the last menstrual period, even though conception typically occurs about two weeks later. This is why a person who is described as 8 weeks pregnant has usually had about 6 weeks of embryonic or fetal growth. Early ultrasound can […]

Key milestones and baby development by trimester

Key milestones and baby development by trimester

Why trimester milestones matter Trimester milestones help organize a complex biological process into clinically meaningful phases. In the earliest weeks, the embryo establishes essential body plans and organs. By mid-pregnancy, fetal structures are large enough for detailed assessment, and many parents begin to feel movement. In late pregnancy, the fetus gains weight, refines neurologic function, […]