Meconium consists of ingested amniotic fluid, cellular debris, mucus, and bile. During approximately weeks 16—20, as the fetus grows and limb movements become more powerful, the mother may begin to feel quickening , or fetal movements.
Sebaceous glands coat the skin with a waxy, protective substance called vernix caseosa that protects and moisturizes the skin and may provide lubrication during childbirth. A silky hair called lanugo also covers the skin during weeks 17—20, but it is shed as the fetus continues to grow. Extremely premature infants sometimes exhibit residual lanugo.
Developmental weeks 21—30 are characterized by rapid weight gain, which is important for maintaining a stable body temperature after birth.
The bone marrow completely takes over erythrocyte synthesis, and the axons of the spinal cord begin to be myelinated, or coated in the electrically insulating glial cell sheaths that are necessary for efficient nervous system functioning.
The process of myelination is not completed until adolescence. During this period, the fetus grows eyelashes.
The eyelids are no longer fused and can be opened and closed. The lungs begin producing surfactant, a substance that reduces surface tension in the lungs and assists proper lung expansion after birth. Inadequate surfactant production in premature newborns may result in respiratory distress syndrome, and as a result, the newborn may require surfactant replacement therapy, supplemental oxygen, or maintenance in a continuous positive airway pressure CPAP chamber during their first days or weeks of life.
In male fetuses, the testes descend into the scrotum near the end of this period. The fetus at 30 weeks measures 28 cm 11 in from crown to rump and exhibits the approximate body proportions of a full-term newborn, but still is much leaner. Visit this site for a summary of the stages of pregnancy , as experienced by the mother, and view the stages of development of the fetus throughout gestation. At what point in fetal development can a regular heartbeat be detected?
The fetus continues to lay down subcutaneous fat from week 31 until birth. The added fat fills out the hypodermis, and the skin transitions from red and wrinkled to soft and pink. Lanugo is shed, and the nails grow to the tips of the fingers and toes. Immediately before birth, the average crown-to-rump length is Once born, the newborn is no longer confined to the fetal position, so subsequent measurements are made from head-to-toe instead of from crown-to-rump. At birth, the average length is approximately 51 cm 20 in.
Throughout the second half of gestation, the fetal intestines accumulate a tarry, greenish black meconium. Unlike these later stools, meconium is sterile; it is devoid of bacteria because the fetus is in a sterile environment and has not consumed any breast milk or formula.
Typically, an infant does not pass meconium until after birth. However, in 5—20 percent of births, the fetus has a bowel movement in utero, which can cause major complications in the newborn. The passage of meconium in the uterus signals fetal distress, particularly fetal hypoxia i. This may be caused by maternal drug abuse especially tobacco or cocaine , maternal hypertension, depletion of amniotic fluid, long labor or difficult birth, or a defect in the placenta that prevents it from delivering adequate oxygen to the fetus.
Meconium passage is typically a complication of full-term or post-term newborns because it is rarely passed before 34 weeks of gestation, when the gastrointestinal system has matured and is appropriately controlled by nervous system stimuli.
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Growing pains 5 fast facts. Thai Chicken Soup. One Pot Mac and Cheese. Chocolate Chip Blondies. Stages of fetal development. This means your period is counted as part of your pregnancy — even though you weren't pregnant at the time. During fertilization, the sperm and egg unite in one of the fallopian tubes to form a zygote. Then the zygote travels down the fallopian tube, where it becomes a morula.
Once it reaches the uterus, the morula becomes a blastocyst. The blastocyst then burrows into the uterine lining — a process called implantation. The sperm and egg unite in one of your fallopian tubes to form a one-celled entity called a zygote.
If more than one egg is released and fertilized or if the fertilized egg splits into two, you might have multiple zygotes. The zygote typically has 46 chromosomes — 23 from the biological mother and 23 from the biological father. These chromosomes help determine your baby's sex and physical traits. Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it will begin dividing to form a cluster of cells resembling a tiny raspberry — a morula.
The rapidly dividing ball of cells — now known as a blastocyst — has begun to burrow into the uterine lining endometrium. This process is called implantation. Within the blastocyst, the inner group of cells will become the embryo. The outer layer will give rise to part of the placenta, which will nourish your baby throughout the pregnancy. By the end of the fifth week of pregnancy — three weeks after conception — your hormone levels are rising. The fifth week of pregnancy, or the third week after conception, the levels of HCG hormone produced by the blastocyst quickly increase.
This signals your ovaries to stop releasing eggs and produce more estrogen and progesterone. Increased levels of these hormones stop your menstrual period, often the first sign of pregnancy, and fuel the growth of the placenta.
The embryo is now made of three layers. The top layer — the ectoderm — will give rise to your baby's outermost layer of skin, central and peripheral nervous systems, eyes, and inner ears. Your baby's heart and a primitive circulatory system will form in the middle layer of cells — the mesoderm. This layer of cells will also serve as the foundation for your baby's bones, ligaments, kidneys and much of the reproductive system. The inner layer of cells — the endoderm — is where your baby's lungs and intestines will develop.
By the end of the sixth week of pregnancy — four weeks after conception — small buds appear that will become arms.
Growth is rapid this week. Just four weeks after conception, the neural tube along your baby's back is closing.
The baby's brain and spinal cord will develop from the neural tube. The heart and other organs also are starting to form. Structures necessary to the formation of the eyes and ears develop. Small buds appear that will soon become arms. The zygote contains all of the genetic information DNA needed to become a baby.
Half the DNA comes from the mother's egg and half from the father's sperm. The zygote spends the next few days traveling down the fallopian tube.
During this time, it divides to form a ball of cells called a blastocyst. A blastocyst is made up of an inner group of cells with an outer shell. The inner group of cells will become the embryo. The embryo is what will develop into your baby. The outer group of cells will become structures, called membranes, which nourish and protect the embryo.
Week 4 Once the blastocyst reaches the uterus, it buries itself in the uterine wall. At this point in the mother's menstrual cycle, the lining of the uterus is thick with blood and ready to support a baby.
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