Session 7 foetal physiology, growth and development

• Pregnancy is counted from the first day of the woman's last period, not the date of conception which generally occurs two weeks later.
• • A pregnancy wheel is also known as a gestation calculator. This is the small calendar that uses your last menstrual period (LMP) to help determine your due date.
  • EDD by LMP is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period.
• • Gestational age is the age of the pregnancy from the last normal menstrual period (LMP)
  • foetal age is the actual age of the growing baby.
• • Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump).
  • Measured between 7 & 13 weeks to date the pregnancy and estimate EDD.
• Dating Scan is used to rule out ectopic pregnancy and to detemine the number of fetuses.
• The Dubowitz/Ballard Examination?

  • evaluates a baby's appearance, skin texture, motor function, and reflexes.
  • Assessment of gestational age of a baby born who did not have any antenatal care
• From week 10 of gestation (week 8 of foetal development) - foetal period.
• Foetal age = Symphysis-fundal height +/- 2cm.
• Trisomy 21: Down Syndrome

  Trisomy 18: Edward Syndrome

  Trisomy 13: Patau syndrome
• Nuchal translucency (NT) is the sonographic appearance of a collection of fluid under the skin behind the foetal neck in the first trimester of pregnancy.
• Nuchal fold thickness - the measurement in second trimester.

  Increased thickness - chromosomal abnormalities
• • combined test: Nuchal translucency (NT), beta-human chorionic gonadotrophin and pregnancy associated plasma protein-A should be offered to screen for Down’s syndrome between 11 and 14 weeks.
  • If it is not possible to do combined test then offer the quadruple test at 14 to 20 weeks: Alpha-fetoprotein (AFP), total human chorionic gonadotrophin (hCG), unconjugated oestriol (uE3) and inhibin-A. Only screens for Downs.
• Bi-Parietal Diameter =The distance between the parietal bones of the foetal skull. Used in combination with abdominal circumference and femur length to assess growth in Trimesters 2 and 3
• dextrocardia - apex more on the right side of the body than left.
• The decidua is the uterine lining during pregnancy. In the non-pregnant uterus the decidua is known as the endometrium.
• The portion of the decidua associated with the placenta is the decidua basalis/placentalis.
• The chorionic plate is made up of the amnion and chorion and forms the boundary of the fetal portion of the placenta.
• Between the chorionic and decidual plate are the intervillous spaces. In the intervillous space there are lakes/lacunae of maternal blood
• The umbilical cord contains 2 arteries carrying deoxygenated blood to the placenta and 1 umbilical vein carrying oxygenated blood back to the baby. These vessels are surrounded by Wharton’s jelly.
• Foetal haemoglobin has a higher affinity for oxygen than maternal Hb.
• Foetal Hb dissociation curve is to the left (higher affinity) of adult Hb. Foetal Hb has lower affinity for 2,3 DPG (results in higher O2 affinity)
• • CO2 passively diffuses from foetal to maternal side. This creates a local acidosis.
  • This local acidosis reduces the oxygen affinity of maternal Hb and oxygen is released to the diffuse to the foetal side and to the foetal Hb. This is the Bohr effect.
• Foetal Blood Flow: The journey

  1. Umbilical Vein carries oxygenated blood from the placenta to the fetus

  2. Ductus Venosus receives oxygenated blood from the umbilical vein, bypasses blood away from the liver and directs it to the inferior vena cava and then to the right atrium

  3. Oxygenated blood goes from IVC (some mixing with blood from lower limbs) into the right atrium

  4. Foramen Ovale is a communication between the two atria, oxygenated Blood flows from right atrium through the foramen ovale to the left atrium, bypassing the lungs

  5. Oxygenated blood goes from LA to LV and then aorta to the brain and upper limbs
• the administration of steroids to a mother with threatened premature delivery is very useful in increasing foetal surfactant production.
• • The increased pulmonary blood flow and pulmonary venous return leads to increase in left atrial pressure (now greater than RA) causing the foramen ovale to close.
  • The ductus arteriosus closes soon after birth in response to increased oxygen tension and reduced prostaglandins (metabolised in pulmonary circulation)
  • The umbilical cord is cut, the arteries go into spasm and the blood flow in the umbilical vein stops and the Ductus venosus closes.