The content provided here is for educational and informational purposes only and should not be considered medical advice, diagnosis, or treatment. Every pregnancy and medical situation is unique. Please consult your OB-GYN or a qualified healthcare professional regarding any questions, concerns, symptoms, or decisions related to your health or pregnancy. Never disregard professional medical advice or delay seeking care because of something you have read here.
Understanding how your baby grows and develops during each trimester can deepen your connection with this incredible process. Let’s take a closer look at the key developmental stages your baby goes through during pregnancy.
First Trimester: The Foundation
The first trimester is a time of rapid development. It’s when your baby forms the foundation for all the vital structures and organs.
Weeks 1-4: Conception and Implantation
Although technically not yet pregnant, during the first two weeks your body is preparing for the possibility of conception. Ovulation occurs, and if the egg meets sperm, fertilization happens.
The egg is fertilized at some point during the third or fourth week. Now a zygote, the fertilized egg travels down the fallopian tube and implants itself in the uterine lining. The zygote becomes a blastocyst, starting the process of cell division and differentiation.
Weeks 5-8: Embryonic Development
During the fifth week, your baby is now called an embryo. Major organs and systems begin to develop. The neural tube, which becomes the brain and spinal cord, starts forming.
Throughout weeks six and seven, the heart begins to beat, tiny buds that will become arms and legs appear, and the brain, eyes, and ears start to develop. By the end of the seventh week, the umbilical cord is fully formed, providing essential nutrients.
Week 8 is when your baby’s facial features begin to form. He or she is about the size of a raspberry at this point.
Weeks 9-12: Fetal Stage
By week nine, the embryo is now considered a fetus. All major organs are present, but they still have a lot of growing and development to do.
During weeks 10 and 11, fingernails and toenails start to form, and your baby can make small movements, although you won’t feel this yet. Your baby’s head makes up nearly half of its length and their external genitalia begin to develop.
During week 12, reflexes like sucking and swallowing develop. Your baby is about 2.5 inches long and weighs about half an ounce.
Second Trimester: Growth and Refinement
The second trimester is often regarded as the most enjoyable part of pregnancy. Your hormones start to even out now that the placenta is fully developed, and some women experience relief from nausea and morning sickness. As your baby grows rapidly, you’ll start to feel their movements.
Weeks 13-16: Rapid Growth
Your baby’s fingerprints are forming, and their bones start to harden during week 13. In weeks 14 and 15, their kidneys produce urine, your baby can make facial expressions, and their hair, eyebrows, and eyelashes begin to grow. Your baby can even hear your heartbeat and outside sounds.
By week 16, your baby is about 4.5 inches long and weighs around 3.5 ounces. You might feel the first flutters of movement, known as quickening.
Weeks 17-20: Active Movements
During week 17, your baby’s skeleton is transformed from cartilage to bone and fat stores begin to develop. By week 18, their ears are in their final position and the nervous system is maturing.
Weeks 19 and 20 mark the halfway point. Vernix caseosa, a protective coating, forms on the skin. They are about 6 inches long and weigh about 8.5 ounces. Their senses are becoming more refined, and they can react to light and sound.
Weeks 21-24: Sensory Development
At weeks 21 and 22, your baby’s movements become more coordinated and they can suck their thumb. Their taste buds are developing, making it possible for them to taste the amniotic fluid.
During weeks 23 and 24, their lungs are developing rapidly, helping prepare them for breathing after birth. Their facial features are also becoming more defined, and they weigh about 1.3 pounds and are around 12 inches long.
Third Trimester: Final Preparations
The third trimester is a time of rapid weight gain and final preparations for life outside the womb. Many women tend to experience swelling in their hands and feet and may find it difficult to find a comfortable sleeping position.
Weeks 25-28: Building Strength
By week 25, your baby’s skin is becoming less translucent, and they can now open and close their eyes. At week 26, their lungs continue to mature and their brain is developing rapidly.
Week 27 brings a fully developed hearing and your baby can recognize your voice. By week 28, your baby is about 14.8 inches long and weighs about 2.2 pounds. They also continue practicing breathing movements, preparing for life outside the womb.
Weeks 29-32: Gaining Weight
At weeks 29 and 30, your baby’s bones are fully developed but are still soft, and they start to gain more body fat. Their brain is also forming grooves and folds, rapidly increasing in size.
By week 31, your baby’s movements may feel more pronounced as they start to run out of space. And by week 32, your baby weighs about 3.7 pounds and is around 16.7 inches long. The fine hair covering their body begins to disappear.
Weeks 33-36: Final Touches
At weeks 33 and 34, your baby’s pupils can react to light, and they continue to gain weight. Their immune system is also developing, preparing for life outside the womb.
Your baby’s nails reach the tips of their fingers and toes by week 35. And by week 36 they are about 18.7 inches long and weigh around 5.8 pounds. They are also getting ready for birth by getting into the head-down position.
Weeks 37-40: Ready for Birth
Your baby is considered full-term by week 37, but they will continue to build fat layers until they are born. At weeks 38 and 39, their brain and lungs are maturing, and they continue to practice swallowing and breathing.
At week 40 your baby is ready to meet you! Depending on development, the average baby weighs around 7.5 pounds and is about 20 inches long.
Embracing the Journey
Pregnancy is a unique and beautiful journey filled with awe-inspiring moments as you witness your baby’s growth and development. Each trimester brings its own milestones and joys, from the first heartbeat to those tiny kicks and hiccups.
At Mary’s Refuge, we celebrate these moments with you, providing a supportive and nurturing environment where you can embrace the journey of motherhood with confidence and love. Remember, you are never alone on this path – we are here to walk beside you every step of the way.
Are you a mother-to-be who feels like they’re not being listened to, have nowhere to turn, and have no safe place to be?
Mary’s Refuge is a sanctuary for young expectant mothers who need a hand up. Our community-building program provides a stable, safe place to live during pregnancy, access to resources for prenatal care and counseling, along with career and educational opportunities. Applicants must be clean and sober, currently pregnant, and have no debilitating medical issues. Feel free contact us online using our confidential form or call us directly at 304.350.1632. We service Martinsburg, WV and the surrounding areas.