Prenatal Development

Conception

  • Ovum is released from the ovary and drawn into the fallopian tube

  • Ovarian hormones prepare the uterine lining for implantation

  • Fertilization occurs in the fallopian tube

  • Sperm meets ovum, forming a zygote

  • The zygote undergoes cell division while traveling to the uterus

  • By approximately day 4, the zygote develops into a blastocyst

    • Inner cell mass (embryonic disc): develops into the fetus

    • Outer layer (trophoblast): provides protection and contributes to placenta formation

Germinal Period (Week 1-2)

  • The zygote develops into a blastocyst

  • Implantation

    • blastocyst attaches to the uterine wall

  • Formation of supportive structures begins:

    • Amnion

    • chorion

    • yolk sac

    • Placenta

    • umbilical cord

Period of Embryo

  • Embryonic Development: Weeks 3–4

  • Measures approximately 6 mm

  • Early development of:

    • Heart

    • Muscles

    • Ribs

    • Backbone

    • Digestive tract

  • Embryonic development: Weeks 5-6

  • Measures approximately 1 inch and 4 grams

  • External body features begin to form

  • Internal organs continue developing

  • Neuron production and migration begin

  • Development of:

    • Sense of touch

    • Movement

Period of Fetus

  • Measures approximately 3 inches in length and less than 1 ounce in weight

  • Rapid increase in overall size

  • Continued development of:

    • Nervous system

    • Organs

    • Muscles

  • Emergence of early behavioral capacities

    • Kicking

    • Thumb sucking

    • Mouth opening

    • Practice (rehearsal) breathing

  • External genitalia become distinguishable

Second Trimester

  • Week 13-24

  • Measured around 12 inches and 1.8 pounds

  • Significant increase in overall size

  • Mother begins to feel fetal movement

  • Most brain neurons are well developed in 24 weeks

  • Sensory development

    • Sensitivity to light

    • Responses to sound

Third Trimester

  • Week 25-38

  • Measures approximately 20 inches in length and 7.5 pounds in weight

  • Continued increase in overall size

  • Organ and system maturation

    • Lungs mature

    • Rapid brain development, especially in neural connectivity

    • Formation of a layer of fat under the skin

    • Transfer of maternal antibodies

  • Rotation into the birth position in preparation for delivery

Prenatal Environmental Influence

Drugs Exposure

  • Prevalence of substance use disorders during pregnancy

  • Studies indicate that approximately 6%-8% of pregnant women in the U.S. have a diagnosable substance use disorder (AUD)

  • Most prevalent substances:

    • Nicotine dependence

    • Cannabis use disorder

    • Opioid use disorder (OUD)

  • Increased health risks for mother and infant, including:

    • Neonatal withdrawal syndrome

    • Preterm birth

    • Low birth weight

  • Maternal complications

    • Hemorrhage

    • Placental abruption

    • Increased mortality risk

Fetus with Alcohol Withdrawal Syndrome

  • Facial abnormalities, including:

    • Short eyelid openings

    • Thin upper lip

    • Smooth or flattened indentation between the nose and upper lip

  • Impaired physical growth

  • Impaired brain growth or brain injury

  • Cognitive and behavioral impairments

  • Approximately 3% of infants are affected by alcohol exposure

Infections

  • AIDS:

    • risk for miscarriage

    • intellectual disabilities

    • low birth weight or premature birth

  • Syphilis:

    • risk for miscarriage

    • physical malformations

    • intellectual disabilities

  • Rubella, HSV2 & toxoplasmosis:

    • risk for miscarriage

    • physical malformations

    • intellectual disabilities

    • low birth weight and prematurity

Maternal Stess

  • Emotional stress can affect both the mother and the pregnancy outcomes

  • Maternal stress hormones are transmitted through the placenta

  • Potential negative behavioral outcomes for the child:

    • Anxiety

    • Depression

    • Attention span difficulties