As an expectant parent, one of the most exciting aspects of pregnancy is tracking the growth and development of your baby. Understanding the size of your baby by week can help you prepare for the upcoming arrival and appreciate the miraculous changes taking place inside your womb. Here, we’ll delve into the fascinating world of fetal development, exploring the average size of babies at different stages of pregnancy.
Embryonic Stage (Week 1-8)
During the initial weeks, your baby is called an embryo. This stage is crucial for the formation of major organs and body systems.
- Week 1-2: The embryo is tiny, about the size of a speck, implanting itself into the uterine lining.
- Week 3-4: The embryo is now around 0.2 inches (5 mm) long, with the beginnings of a neural tube, which will become the brain and spinal cord.
- Week 5-6: At approximately 0.25 inches (6-7 mm) long, the embryo’s heart starts beating, and limb buds appear.
- Week 7-8: The embryo measures about 0.5-0.6 inches (13-15 mm) in length, with more defined limbs and fingers.
Fetal Stage (Week 9-38)
By week 9, the embryo is now referred to as a fetus, marking a period of rapid growth and refinement of features.
- Week 9-10: The fetus is about 1.2 inches (3 cm) long and weighs 0.07 ounces (2 grams). Its toes and fingers are webbed, but the pancreas starts producing digestive enzymes.
- Week 11-12: Measuring around 2.1-2.5 inches (5.5-6.5 cm) in length and weighing about 0.25 ounces (7 grams), the fetus’s skin is translucent, and its skeleton is made of soft cartilage.
- Week 13-14: At approximately 3.5 inches (8.9 cm) long and 0.81 ounces (23 grams) in weight, the fetus can swallow and kick. Its skin starts to thicken, and fat layers form.
- Week 15-16: Now about 4.5-4.9 inches (11.5-12.5 cm) in length and weighing 2.5-3.5 ounces (70-100 grams), the fetus’s pancreas starts producing insulin, and its skin starts to thicken more.
Second Trimester (Week 17-27)
- Week 17-18: The fetus measures around 5.5 inches (14 cm) long and weighs 5.9 ounces (170 grams). It can detect light and darkness.
- Week 19-20: At about 6-6.7 inches (15.2-17 cm) in length and 8.5-10.2 ounces (240-290 grams) in weight, the fetus’s nervous system matures, and it starts to store fat.
- Week 21-22: Measuring 7-7.7 inches (17.8-19.6 cm) and weighing around 12.7 ounces (360 grams), its skin thickens, and fat layers increase for insulation.
- Week 23-24: Now about 8-8.7 inches (20-22 cm) in length and weighing 1.3 pounds (590 grams), the fetus has a more defined skin texture, and its pancreas is functioning.
- Week 25-26: At approximately 9-9.7 inches (22.8-24.6 cm) long and weighing 1.5 pounds (680 grams), the fetus can detect sounds outside the womb, such as the mother’s voice.
- Week 27: Measuring around 10 inches (25.4 cm) and weighing 2 pounds (910 grams), the fetus is preparing for life outside, with its lungs starting to produce surfactant, a substance that helps them expand properly after birth.
Third Trimester (Week 28-40)
- Week 28: The fetus is approximately 10 inches (25.4 cm) long and weighs about 2.2 pounds (1 kg).
- Week 29-30: Measuring 10.5-11.4 inches (26.7-28.9 cm) and weighing around 2.9-3.3 pounds (1.3-1.5 kg), its skin becomes thicker, and fat layers increase.
- Week 31-32: At about 11-11.8 inches (28-30 cm) in length and weighing 3.5-4 pounds (1.6-1.8 kg), the fetus’s bones are starting to harden, and its nervous system is maturing.
- Week 33-34: Now around 12-12.6 inches (30.5-32 cm) long and weighing approximately 4.7-5.3 pounds (2.1-2.4 kg), the fetus’s lungs continue to mature.
- Week 35-36: Measuring about 12.6-13.5 inches (32-34.3 cm) and weighing 5.7-6.3 pounds (2.6-2.9 kg), the fetus’s eyes can open and close, and it practices breathing.
- Week 37-38: At approximately 13.5-14.2 inches (34.3-36 cm) in length and weighing around 6.3-7 pounds (2.9-3.2 kg), the fetus is almost fully developed and gains about a half pound per week.
- Week 39-40: The full-term fetus measures about 14-14.5 inches (35.6-36.8 cm) and weighs between 7-8 pounds (3.2-3.6 kg), with some variation in size due to individual development.
Conclusion
Understanding your baby’s size by week is a fascinating journey through fetal development, showcasing the incredible journey from a tiny embryo to a fully formed baby. Each stage is filled with remarkable milestones and growth, and tracking these developments can make the waiting period more engaging and informative for expectant parents. Whether you’re weeks into your pregnancy or nearing the due date, knowing the size and development stage of your baby can help you connect better with the little one on the way.
