BGDA Practical 12 - Birth

From Embryology
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Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Introduction

Historic model of birth process (Galletti, 1770)
Australian-births 2007.png

Birth or parturition is a critical stage in development, representing in mammals a transition from direct maternal support of fetal development, physical expulsion and establishment of the newborns own respiratory, circulatory and digestive systems. These notes only cover the biological processes surrounding birth including fetal signaling changes and maternal signaling changes. Note that there is a growing worldwide trend in developed countries toward caesarean section delivery. There are a great number of comprehensive, scientific and general, books and articles that cover birth, childbirth or parturition. The time surrounding birth is known as the perinatal period.

BrauneB1.jpg

Position of the Uterus and Fetus at Term (Braune, 1877)

Childbirth

  • Parturition (Latin, parturitio = "childbirth") describes expelling the fetus, placenta and fetal membranes and is probably initiated by fetus not mother.
  • Preterm birth - Risks of preterm birth in abnormal low birth weight (intrauterine growth restriction) and high (large for gestational age) categories are 2- to 3-fold greater than the risk among appropriate-for-gestational-age infants.
  • Maternal labor - uterine contractions and dilation of cervix, process under endocrine regulation
  • Placenta and fetal membranes - (Latin, secundina = "following") expelled after neonate birth

Uterine Myometrial Changes

  • Smooth muscle fibers - hypertrophy not proliferation
  • Stretching of myometrium - stimulates spontaneous muscular contraction, during pregnancy progesterone inhibits contraction
  • Stimulating contraction - increased estrogen levels (placental secretion sensitizes smooth muscle), increased oxytocin levels (fetal oxytocin release- force and frequency of contraction), fetal pituitary prostaglandin production (estrogen and oxytocin stimulate endometrial production of prostaglandin)
Hormones Roles
Progesterone
  • maintains pregnancy - initially synthesized by corpus luteum, then levels maintained by placenta
  • hyperpolarizes myometrial cells (-65 mV), reduces excitability and conductivity
  • Level in plasma may fall just before parturition, definitely decreases following delivery of placenta
Estrogens
  • Group of steroidal hormones, peak when parturition begins
  • induce increased synthesis of actomyosin and ATP in myometrial cells
  • alter membrane potential (-50 Mv) enhances excitation/conduction
  • act to directly increase myometrial contraction
  • indirectly by increasing oxytocin from pituitary gland
  • Estriol - synthesized by fetus and placenta
Oxytocin
  • Peptide hormone (8aa) from maternal posterior pituitary, initiation and maintenance of labour (synthetic form labour induction)
  • myometrium sensitivity to oxytocin (increased by estrogen, decreased by progesterone)
  • stimulus for release - mechanical stimulation of uterus, cervix and vagina (ethanol inhibits release)
Prostaglandins
  • hydroxy fatty acids - sythesized by placenta, amniotic fliud contains mainly PGF2 alpha, causes myometrial contraction (also in maternal plasma)
  • prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) - used to induce labour (intravenous, oral, intravaginal, intraamniotic)
  • Aspirin inhibitor of PG synthesis - leads to increased duration of pregnancy
Endocrine Birth

External Environment

  • mainly shown in other species parturition occurs in peaceful undisturbed surroundings, stress may have an inhibitory effect on oxytocin release
  • Most human births occur at night (peak at 3 am) diurnal rhythm influence

Labour Stages

Birth Stage 2
Labour Stages Changes Time Roles
Stage 1 Dilatation 7 to 12 hours
longer for first child
Uterine contractions 10 minutes apart, function to dilate cervix fetal membranes rupture releasing amnion.
Stage 2 Expulsion 20 to 50 minutes Uterine contractions 2 to 3 minutes apart, function to push fetus through cervix and vagina.
Stage 3 Placental 15 minutes Uterine contractions following child delivery expel placenta. Haematoma separates placenta from uterine wall, separation occurs at spongy layer of decidua basalis.
Stage 4 Recovery 2+ hours Uterine contractions continue and myometrial contraction closes spiral arteries, also begins to reduce uterine volume.
Birth- Magnetic Resonance Imaging 02.jpg The birth of a child in an “open” MRI (magnetic resonance imaging) scanner that allows a mother-to-be to fit fully into the machine.


Birth MRI icon.jpg
 ‎‎Human Birth MRI
Page | Play

Birth Method

Method of Birth (Australia, 2007)

  • 57.9% vaginal births
  • 11.2% had an instrumental vaginal delivery (forceps or vacuum extraction)
  • 30.9% caesarean section births
    • 21.1% in 1998, 30.8% in 2006, rate recently stable
    • 83.3% of these were repeat caesarean sections
Australian birth delivery method

Birth - Caesarean

The rate of caesarean delivery (c-section or C/S) compared to normal vaginal birth is variable between countries (12-25%) and increasing, particularly in older women. There are a number of different explanations as to why this is occuring, including maternal or fetal complications of either development or delivery. The World Health Organization (WHO) recommended rate (10 - 15%).

Birth caesarean


Links: Birth - Caesarean Delivery

Birth Weights

Human Birth Weight Classifications
no colour
Birth weight (grams) less 500 500 – 999 1,000 – 1,499 1,500 – 1,999 2,000 – 2,499 2,500 – 2,999 3,000 – 3,499 3,500 – 3,999 4,000 – 4,499 4,500 – 4,999 5,000 or more
Classification
Extremely Low Birth Weight
Very Low Birth Weight
Low Birth Weight
Normal Birth Weight
High Birth Weight

The primary causes of VLBW are premature birth (born <37 weeks gestation, and often <30 weeks) and intrauterine growth restriction (IUGR), usually due to problems with placenta, maternal health, or to birth defects. Many VLBW babies with IUGR are preterm and thus are both physically small and physiologically immature.

Birthweight (Australia, 2007)

Fetal weight change
  • 92.1% of liveborn babies had a birthweight in the range 2,500–4,499 grams
    • average birthweight was 3,374 grams
  • 17,976 (6.2%) low birthweight (weighing less than 2,500 grams)
  • 2,956 (1.0%) very low birthweight (weighing less than 1,500 grams)
  • 1,288 (0.4%) extremely low birthweight (weighing less than 1,000 grams)

Data: Australia’s mothers and babies 2007 AIHW Perinatal statistics series no. 23




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Practical 12: Embryo to Fetus | Second Trimester | Third Trimester | Birth | Neonatal | Abnormalities


Birth Terms

Birth

  • amniotomy - birth medical procedure thought to speed labor, where the amniotic sac is artificially ruptured using a tool (amniohook).
  • birth - (parturition, partus, childbirth, labour, delivery). expulsion of the foetus from the uterus. (More? Birth)
  • birth weight - (birth-weight) the weight of the neonate measured as soon as possible after birth. (More? Birth Weight)
  • Bishop score - (Bishop's score) A clinical test prior to birth named after the obstetrician/gynaecologist Edward H. Bishop (1913-1995) who published a 1964 paper "Pelvic Scoring For Elective Induction". (More? PMID 14199536)
  • breech - fetal buttocks presented first and can also occur in different forms depending on presentation (complete breech, frank breech, footing breech, knee breech).
  • decidual activation - increased uterine proteolysis and extracellular matrix degradation.
  • dilatation - opening of the cervix in preparation for birth (expressed in centimetres).
  • effacement - shortening or thinning of the cervix, in preparation for birth.
  • forceps - mechanical "plier-like" tool used on fetal head to aid birth.
  • labor - the maternal physiological process of birth. (More? Birth)
  • macrosomia - clinical description for a fetus that is too large, condition increases steadily with advancing gestational age and defined by a variety of birthweights. In pregnant women anywhere between 2 - 15% have birth weights of greater than 4000 grams (4 Kg, 8 lb 13 oz). (More? Macrosomia)
  • membrane rupture - breaking of the amniotic membrane and release of amniotic fluid (water breaking).
  • morbidity - (Latin, morbidus = "sick" or "unhealthy") refers to a diseased state, disability, or poor health due to any cause.
  • neonatal - the early postnatal period relating to the birth, it includes the period up to 4 weeks after birth.
  • obstetric fistula - abnormal connection between the vagina and rectum or bladder caused by a prolonged obstructed labor.
  • perinatal - the early postnatal period relating to the birth, statistically it includes the period up to 7 days after birth.
  • presentation - how the fetus is situated in the uterus.
  • presenting part - part of fetus body that is closest to the cervix.
  • second stage of labour - passage of the baby through the birth canal into the outside world.
  • vacuum extractor - (ventouse) rubber or metal suction cap device used on fetal head to aid birth.
  • vertex presentation - (cephalic presentation) where the fetus head is the presenting part, most common and safest birth position.
Other Terms Lists  
Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Gastrointestinal | Genetic | Hearing | Heart | Immune | Integumentary | Neural | Oocyte | Palate | Placenta | Renal | Respiratory | Spermatozoa | Ultrasound | Vision | Historic | Glossary

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.
Birth Links: Introduction | Lecture - Birth | Caesarean | Preterm | Birth Weight | Birth Statistics | Australian Birth Data | Developmental Origins of Health and Disease | Macrosomia | Neonatal Diagnosis | Apgar test | Guthrie test | Neonatal Development | Stillbirth and Perinatal Death | ICD-10 Perinatal Period | Category:Birth

Historic Birth Models

About The Models - a series of models commissioned by Giuseppe Galletti (? - 1819) currently held in the Institute and Museum of the History of Science (Italy) Istituto e Museo di Storia della Scienza (IMSS). Giuseppe Galletti and others used terracotta and wax models that he had commissioned in Florence between 1770 and 1775 to train surgeons and midwives.

Premature Birth

Premature infant
Year < 34 weeks % 34-36 weeks % total preterm %
1990 3.3 7.3 10.6
1995 3.3 7.7 11
2000 3.4 8.2 11.6
2005 3.6 9.1 12.7

Stillbirths

Commentary: reducing the world's stillbirths. Goldenberg RL, McClure EM, Belizán JM. BMC Pregnancy Childbirth. 2009 May 7;9 Suppl 1:S1. PMID: 19426464 | PMC2679407

"One of the major success stories of modern obstetrics in high-income countries in the last 5 decades is the reduction of stillbirths from rates as high as 50 per 1000 births to about 5 per 1000 births today. Fetal mortality associated with obstructed labour, asphyxia, hypertension, diabetes, Rh disease, placental abruption, post-term pregnancies and infections such as syphilis all have declined. Much of this success has occurred in term births in the intrapartum period so that most stillbirths in high-income countries now occur in the antepartum period and are pre-term."
Links: Stillbirth and Perinatal Death


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Cite this page: Hill, M.A. 2017 Embryology BGDA Practical 12 - Birth. Retrieved November 18, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_12_-_Birth

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G