Conception and Prenatal Development

Conception and Prenatal Development

Human Conception Process

  1. Conception Steps

    • STEP 1: Ovulation

      • Definition: The release of a mature egg from the ovary for possible fertilization.

      • When: About 14 days before next menstrual period.

      • Where: Occurs in the fallopian tube.

      • Duration: The egg remains viable for 12-24 hours.

    • STEP 2: Fertilization

      • Definition: The union of the sperm with the egg, also known as conception.

      • When: Occurs during the 12-24 hours following ovulation.

      • Where: Takes place in the fallopian tube, near the ovary.

      • Duration: Fertilization process can last up to 24 hours.

    • STEP 3: Implantation

      • Definition: The attachment of the fertilized egg, now referred to as a blastocyst, to the uterine wall.

      • When: Happens about 6-11 days after fertilization.

      • Where: Occurs in the uterine lining.

      • Duration: The implantation process can take up to 48 hours.

Normal Prenatal Development

  1. Fetal Development

    • Period: From 9 weeks through birth.

    • Full Term: 36-40 weeks of fertilized age.

    • Gestational Age: 38-42 weeks.

    • Important Note: It is crucial to review relevant tables regarding fetal development at this stage to understand the growth trajectory.

Auxiliary Structures in Prenatal Development

  1. Placenta

    • Permits exchange across two vascular systems:

      • Functions include:

        • Metabolic: Supports metabolism of the fetus.

        • Transfer of substances: Facilitates the transfer of nutrients and waste products between mother and fetus.

        • Endocrine: Produces hormones necessary for maintaining pregnancy.

        • Perfusion: Supplies oxygen and removes carbon dioxide from the fetal blood.

  2. Fetal Membranes

    • Two main membranes:

      • Amnion: Provides a protective amniotic sac for the fetus.

      • Chorion: Contributes to the formation of the placenta.

    • Umbilical Cord: Connects the fetus to the placenta, allowing nutrient and waste exchange.

    • Fetal Circulation: Encompasses all blood flow systems within the fetus arranged around the umbilical cord and membranes.

Prenatal and Post-Birth Circulation

  1. Fetal Circulatory Circuit

    • Components of the fetal circulation include:

      • Aortic arch

      • Superior vena cava

      • Ductus arteriosus

      • Right atrium (non-inflated lung condition)

        • Foramen ovale: An opening in the heart allowing blood to bypass the non-functioning lungs, kept open during fetal life.

      • Inferior vena cava

      • Ductus venosus

      • Aorta

      • Liver

      • Umbilical cord: Contains blood vessels that connect the fetus to the placenta.

      • Placenta: The organ providing nutrient exchange.

      • Portal vein & Umbilical veins: Transport oxygenated blood from the placenta to the fetus.

      • Umbilical arteries: Carry deoxygenated blood back to the placenta.

    • Key to Oxygen Saturation of Blood:**

      • High: Areas with a high level of oxygen saturation.

      • Medium: Intermediate levels of oxygen saturation.

      • Low: Areas with low levels of oxygen saturation.

  2. Circulation After Birth

    • Changes occur where

      • The Foramen ovale closes, redirecting blood flow as the lungs become functional.

      • Right atrium now receives blood from the inferior vena cava with the lungs inflated.

      • Components like the ligamentum teres (formerly umbilical vein) and medial umbilical ligaments (formerly umbilical arteries) become remnants of fetal circulation.

      • The ligamentum arteriosum (formerly ductus arteriosus) and ligamentum venosum (formerly ductus venosus) are formed post-birth.

      • Blood flow now follows a different route, significantly altering the blood saturation levels compared to fetal life.

Deviations from Normal Conception and Prenatal Development

  1. Multifetal Pregnancy

    • Types observed:

      • A: Zygote stage showing two-cell stage with regards to two amniotic sacs but one placenta and one chorionic sac.

      • B: Blastocyst stage indicating implantation with separate chorionic and amniotic sacs resulting from two zygotes each reaching the two-cell stage.