Pregnancy is an exciting journey that involves dramatic changes for both the expectant mother and the developing baby. As each week passes, new developments occur, bringing mothers closer to the moment they meet their baby. Here’s a week-by-week guide that walks through the various stages of pregnancy, from conception to birth.
Weeks 1-4: Conception and Early Development
The Start of Life
Pregnancy officially begins on the first day of the woman’s last menstrual period (LMP), even though conception happens about two weeks later.
During these early weeks, fertilization occurs when the sperm meets the egg, forming a zygote. The zygote travels down the fallopian tube and implants itself in the uterus, where it will grow into an embryo.
Many women may not yet realize they are pregnant during this period, as symptoms are often minimal.
Changes in the Mother:
No noticeable physical changes yet, though some women might experience mild cramping or spotting as the embryo implants.
Hormonal changes begin, setting the foundation for pregnancy.
Weeks 5-8: The First Trimester
Embryo Formation
Around week 5, the embryo consists of three layers that will form all of the baby’s organs and tissues.
By week 6, the neural tube, which becomes the brain and spinal cord, is closing, and the heart is beating.
Week 7:
Limb buds start forming, which will become arms and legs.
The embryo is around the size of a blueberry.
Changes in the Mother:
Hormones rise significantly, leading to early pregnancy symptoms like nausea (morning sickness), fatigue, and breast tenderness.
A positive pregnancy test usually occurs by week 5-6 due to rising hCG levels.
Weeks 9-12: Embryo to Fetus
Rapid Growth and Development
By week 9, the embryo is now called a fetus. Its facial features are developing, including eyes, nose, and mouth.
Organs like the liver, kidneys, and intestines are starting to function.
The fetus grows from about the size of a grape in week 9 to nearly the size of a lime by week 12.
Week 12:
The placenta takes over hormone production to sustain the pregnancy.
The fetus's movements can begin, although they are not yet felt by the mother.
Changes in the Mother:
Symptoms like nausea and fatigue often peak around this time.
By the end of week 12, many women find relief as symptoms start to ease.
The uterus begins to expand but may not be visible yet as a baby bump.
Weeks 13-16: Entering the Second Trimester
More Defined Features
During these weeks, the fetus’s facial features become more refined, and bones begin to harden.
The fetus grows to about 4 inches long by week 16, around the size of an avocado.
The baby’s heartbeat can be heard through a Doppler device, and tiny muscles allow it to make small movements.
Week 16:
The baby’s eyes are forming, though they remain closed.
The fetus begins to develop reflexes, such as sucking and swallowing.
Changes in the Mother:
Many women feel an energy boost as the second trimester begins, and morning sickness often subsides.
A visible baby bump may start to appear, and some mothers may begin to feel their baby’s movements (known as “quickening”).
Weeks 17-20: Growth and Movement
Feeling the Baby Move
The baby is growing rapidly during these weeks, with major developments such as the formation of fingerprints and the beginnings of hearing.
By week 20, the baby is about the size of a banana and weighs around 10 ounces.
Week 20:
The halfway point of pregnancy!
The baby’s movements may become more noticeable, and kicks might be felt.
Changes in the Mother:
The uterus has grown enough to be felt at or above the belly button.
Many mothers will have their mid-pregnancy ultrasound around this time, where they can see detailed images of their baby and possibly learn the baby’s sex.
Weeks 21-24: Continued Growth and Viability
Vital Development
The baby’s senses are developing rapidly during these weeks.
By week 24, the baby’s lungs are forming and producing surfactant, which will help the baby breathe after birth.
The baby is gaining weight and fat, preparing for life outside the womb.
Week 24:
The baby weighs about 1.5 pounds and is around a foot long.
The baby’s skin is still translucent but is starting to develop more fat.
Changes in the Mother:
Expectant mothers may feel their baby’s kicks more frequently and clearly.
Stretch marks, swollen feet, and back pain may start to appear as the baby grows.
Weeks 25-28: End of the Second Trimester
Preparing for Life Outside
The baby is now viable, meaning if born prematurely, there’s a good chance of survival with medical intervention.
The brain is developing rapidly, and the baby’s lungs are maturing.
The baby’s eyes are beginning to open and respond to light.
Week 28:
The baby weighs about 2.5 pounds and is about the size of an eggplant.
The baby’s movements are strong, and patterns of waking and sleeping are more noticeable.
Changes in the Mother:
Many women will experience Braxton Hicks contractions (false labor) as the body prepares for delivery.Heartburn, leg cramps, and other discomforts may become more pronounced.
Weeks 29-36: The Third Trimester
Final Growth and Preparation
The baby is rapidly gaining weight, and its organs, especially the lungs, are preparing for life outside the womb.
By week 36, the baby is likely to be head-down, ready for birth.
Week 36:
The baby weighs around 6 pounds and is about 18-20 inches long.
The baby’s reflexes, such as sucking and grasping, are well developed.
Changes in the Mother:
The baby bump is now large, and many mothers experience difficulty sleeping, shortness of breath, and increased fatigue.
Some may experience “lightening,” when the baby drops into the pelvis, relieving pressure on the lungs but increasing pressure on the bladder.
Weeks 37-40: Full Term
Ready for Birth
At 37 weeks, the baby is considered full-term and ready for birth.
The lungs are mature, and the baby’s body continues to grow and develop.
The baby’s weight ranges between 6 to 9 pounds and measures 19 to 21 inches long by week 40.
Changes in the Mother:
Contractions may become more regular as the body prepares for labor.
The mother may feel a burst of energy, known as the “nesting instinct,” as she prepares for the baby’s arrival.
Conclusion
Pregnancy is a miraculous process that involves significant changes for both mother and baby. Understanding the week-by-week developments helps expectant parents track their baby’s progress and prepare for birth. Every pregnancy is unique, and while the journey is full of excitement, it’s essential to stay in close contact with healthcare providers to ensure both mother and baby stay healthy.
