Reproductive Anatomy, Genetics & Genomics, Embryology and Fetal Development
Key Takeaways
Fertilisation usually occurs in the ampulla of the fallopian tube, and the blastocyst implants in the endometrium about 6 to 10 days after fertilisation.
The embryonic period (weeks 3 to 8 after fertilisation) is when organs form, so teratogens such as alcohol and valproate cause the most structural harm then.
The neural tube closes about 28 days after conception, which is why folic acid must be taken before conception and until 12 weeks of pregnancy.
In autosomal recessive conditions such as cystic fibrosis and sickle cell disease, two carrier parents have a 1 in 4 chance of an affected child in each pregnancy.
Fetal circulation uses three shunts (ductus venosus, foramen ovale and ductus arteriosus), which close after birth as the lungs expand and pulmonary resistance falls.
Reproductive Anatomy, Genetics & Genomics, Embryology and Fetal Development
The Future Midwife standards require knowledge of the anatomy, physiology, genetics and genomics of girls and women and of the male reproductive system (3.11), and of fetal development, adaptation to life and very early child development (3.13). Midwives must also recognise complications related to embryology and fetal development (4.4.1). This knowledge underpins preconception advice, screening discussions and explanations of risk.
Female Reproductive Anatomy and Physiology
- Ovaries: produce oocytes and the hormones oestrogen and progesterone. Each ovary contains thousands of follicles at puberty.
- Fallopian tubes: have four parts (interstitial, isthmus, ampulla and the fimbriated infundibulum). Fertilisation usually occurs in the ampulla, and the fimbriae collect the released oocyte.
- Uterus: a muscular organ with a fundus, body and cervix. The wall has three layers: the perimetrium, the myometrium (smooth muscle that contracts in labour) and the endometrium (which thickens each cycle and becomes the decidua in pregnancy). The isthmus forms the lower uterine segment in late pregnancy.
- Blood supply: the uterine arteries arise from the internal iliac arteries, and the ovarian arteries arise directly from the abdominal aorta.
- Vagina and vulva: the vagina is an elastic muscular canal; the vulva includes the labia, clitoris and vestibule.
- Pelvic floor: the levator ani (pubococcygeus, puborectalis and iliococcygeus) and coccygeus support the pelvic organs, and the perineal body is the central anchoring point that can be torn in childbirth.
The Menstrual Cycle
In a typical 28-day cycle:
- Follicular phase: follicle-stimulating hormone (FSH) stimulates follicles, which produce oestrogen and thicken the endometrium (proliferative phase).
- Ovulation: a surge of luteinising hormone (LH) triggers release of the oocyte, around day 14.
- Luteal phase: the corpus luteum produces progesterone, making the endometrium secretory and ready for implantation.
- If pregnancy occurs, human chorionic gonadotrophin (hCG) from the trophoblast maintains the corpus luteum until the placenta takes over progesterone production, at around 10 to 12 weeks. Without pregnancy, progesterone falls and menstruation follows.
Male Reproductive Anatomy
- Testes: lie in the scrotum, about 2°C to 3°C below core body temperature. Seminiferous tubules produce sperm (supported by Sertoli cells), and Leydig cells produce testosterone.
- Epididymis: sperm mature and are stored here.
- Vas deferens: carries sperm to the ejaculatory ducts; it is cut in vasectomy.
- Seminal vesicles and prostate: add fluid that nourishes and protects sperm.
- Spermatogenesis takes roughly two to three months, so lifestyle changes such as stopping smoking take time to improve sperm quality.
- Undescended testes are checked at the newborn examination because they affect fertility and cancer risk later in life.
Genetics, Genomics and Epigenetics
Human cells contain 46 chromosomes in 23 pairs: 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Eggs and sperm are formed by meiosis, which halves the chromosome number. Errors in meiosis (non-disjunction) cause aneuploidy, such as trisomy 21, which becomes more common with increasing maternal age.
| Inheritance Pattern | Risk to Each Child | Examples |
|---|---|---|
| Autosomal dominant | 1 in 2 (50%) if one parent is affected | Huntington's disease, myotonic dystrophy |
| Autosomal recessive | 1 in 4 (25%) if both parents are carriers; 1 in 2 chance of being a carrier | Cystic fibrosis, sickle cell disease, thalassaemia, phenylketonuria |
| X-linked recessive | If the mother is a carrier, each son has a 1 in 2 chance of being affected and each daughter a 1 in 2 chance of being a carrier | Haemophilia A, Duchenne muscular dystrophy |
Consanguinity (parents who are blood relatives) increases the chance that both carry the same recessive variant. Midwives take a family history at booking and refer couples to genetic services when appropriate.
Genomics is the study of a person's whole genetic material. In England, the NHS Genomic Medicine Service offers genomic testing, including rapid whole genome sequencing for seriously ill babies and children to speed diagnosis. Cell-free DNA testing (NIPT) uses fragments of placental DNA in the mother's blood.
Epigenetics describes changes in how genes are switched on or off without changing the DNA sequence, for example through DNA methylation. Maternal nutrition, smoking, stress and diabetes can cause epigenetic changes that influence the baby's long-term health. This underpins the developmental origins of health and disease concept, which links early-life conditions to adult heart disease and diabetes.
Fertilisation, Implantation and Embryology
- Fertilisation in the ampulla forms a zygote.
- The zygote divides as it travels along the tube, forming a morula (about day 3 to 4) and then a blastocyst (about day 5).
- Implantation in the endometrium begins about 6 to 10 days after fertilisation. The outer trophoblast forms the placenta and produces hCG; the inner cell mass forms the embryo.
- Gastrulation in week 3 forms three germ layers:
- Ectoderm: nervous system, skin, hair and the lens of the eye.
- Mesoderm: heart, blood vessels, muscles, bones, kidneys and gonads.
- Endoderm: lining of the gut and airways, liver and pancreas.
- The neural tube closes by about day 28 after conception, which is why folic acid is advised before conception and until 12 weeks.
- The heart begins to beat at about day 22.
The embryonic period (weeks 3 to 8 after fertilisation) is when organs form (organogenesis), so it is the time of greatest vulnerability to teratogens, such as alcohol, sodium valproate, isotretinoin, high-dose vitamin A and some infections. From week 9 after fertilisation, the developing baby is called a fetus. Remember that gestational age is counted from the first day of the last menstrual period, about two weeks before conception.
Fetal Development Milestones
- Movements are usually first felt between about 16 and 20 weeks (later in first pregnancies).
- Surfactant production begins from around 24 weeks, but mature levels are not reached until about 34 to 36 weeks, which is why preterm babies are at risk of respiratory distress.
- Vernix protects the skin, and lanugo (fine hair) appears in mid-pregnancy and is largely shed by term.
Fetal Circulation
The placenta, not the lungs, oxygenates fetal blood. The umbilical vein carries oxygenated blood to the fetus and the two umbilical arteries return deoxygenated blood to the placenta. Three shunts bypass the liver and lungs:
- Ductus venosus: from the umbilical vein to the inferior vena cava.
- Foramen ovale: from the right atrium to the left atrium.
- Ductus arteriosus: from the pulmonary artery to the aorta.
At birth, lung expansion lowers pulmonary vascular resistance, left atrial pressure rises and the foramen ovale closes functionally. The ductus arteriosus constricts over the following days. Persistent pulmonary hypertension of the newborn occurs when this transition fails.
Congenital Anomalies and Screening
Congenital heart disease is the most common major structural anomaly, affecting roughly 8 in every 1,000 babies. The fetal anomaly ultrasound scan (18+0 to 20+6 weeks) in England screens for 11 conditions: anencephaly, open spina bifida, cleft lip, congenital diaphragmatic hernia, gastroschisis, exomphalos, serious cardiac abnormalities, bilateral renal agenesis, lethal skeletal dysplasia, Edwards' syndrome and Patau's syndrome. Two abdominal wall defects are often compared:
- Gastroschisis: bowel herniates through a defect beside the umbilicus with no covering membrane; it is more common in younger mothers and is usually an isolated anomaly.
- Exomphalos: abdominal contents herniate into the umbilical cord and are covered by a membrane; it is often associated with chromosomal or other anomalies.
Midwives explain screening as a choice, support women through results and refer to fetal medicine teams. Sickle cell and thalassaemia screening is offered to all women ideally by 10 weeks, with partner testing if the woman is a carrier.
Very Early Child Development
The brain grows rapidly in the first years of life. Responsive care, skin-to-skin contact, breastfeeding and "serve and return" interactions (responding to a baby's cues) build secure attachment and healthy brain development. Babies typically begin to smile socially at about 6 weeks. Midwives hand over to health visitors, who continue to support development through the Healthy Child Programme.
Both members of a couple are carriers of the cystic fibrosis gene. What is the chance that each of their children will have cystic fibrosis?
1 in 4 (25%) for each pregnancy
1 in 2 (50%) for each pregnancy
3 in 4 (75%) for each pregnancy
There is no risk because carriers do not pass on the gene
Why is the embryonic period (weeks 3 to 8 after fertilisation) the time of greatest risk from teratogens such as sodium valproate and alcohol?
It is when the placenta first allows drugs to reach the fetus
Organogenesis takes place, so the developing organs are most vulnerable to structural damage
The fetus begins to swallow amniotic fluid, concentrating drugs
Surfactant production begins, making the lungs vulnerable to toxins
At birth, which change causes the foramen ovale to close functionally?
Clamping of the umbilical cord increases pressure in the right atrium
The ductus venosus dilates, increasing blood flow to the liver
Lung expansion lowers pulmonary vascular resistance and raises left atrial pressure above right atrial pressure
Rising prostaglandin levels after birth keep the foramen ovale open
Sections you finish are checked off in the contents.