Parturition & Pregnancy Loss

What is precocial offspring?

Offspring that can stand and function immediately after birth, important for prey species

What is altricial offspring?

Offspring that are born unable to survive on their own, predator species

What are some behavioral/physical shifts preceding labor?

Panting, shivering, restlessness, looking at abdomen, nesting, appetite loss, clinginess or seclusion, grooming, etc.

What are some udder developments preceding labor?

Mammary gland swells, wax, dripping milk (colostrum)

What are some vulvar/pelvic developments preceding labor?

Vulva becomes soft, swollen, elongates, mucous discharge, etc.

Pelvic/tail ligament relaxes

What are some hormonal shifts preceding labor?

Progesterone steeply decline, estradiol and prostaglandins/uterotonins increase promoting myometrial contractions

What are the main triggers of labor?

Fetal stress spikes fetal cortisol

What causes fetal stress?

Limited space, increased fetal demands (nutrients and oxygen)

What is the purpose of estrogen increase leading up to birth?

Increases secretions, promotes myometrial contractions (further stresses fetus further promoting labor), increases oxytocin receptor in uterus, etc.

What promotes the conversion from progesterone to estrogen during labor?

Cortisol from fetal stress

What are the direct results of fetal stress spiking?

Fetal stress spiking causes fetal cortisol to rise leading to:

Progesterone to decline and convert to estrogen

PGF2a (luteolysis in some species) increases in turn triggering a surge of relaxin

Myometrial contractions begin

What hormones cause the initial contractions?

PGF2a and estrogen

What hormones cause labor contractions?

Oyxtocin (main), a little bit of : PGF2a and estrogen

What is the Fergusson (ejection) reflex?

Reflex caused by fetal stress → cortisol triggering myometrial contractions → cervical stimulation → oxytocin

What are the 3 stages of labor?

Stage 1: Myometrial contractions

Stage 2: Expulsion of fetus

Stage 3: Expulsion of fetal membranes

What does stage 1: myometrial contractions entail about labor?

Lasts 2-12 hours, myometrial contractions, uterine pressure, abdominal discomfort, cervical dilation, fetal entry into birth canal

What does stage 2: expulsion of fetus entail about labor?

30-180 mins, strong uterine contractions (Fergusson reflex + abdominal contractions), water breaks (allantochorion - pre-delivery, amnion - delivery/post-delivery), appearance of the amnion, rupture of the amnion and delivery, umbilical cord breaks/bitten off (more common in altricial)

What does it mean when the “water breaks”?

The amnion ruptures and amniotic fluid (suspends fetus and protects it from shock) leaks out, occurs during the 2nd stage of labor

How should the fetus typically be positioned during labor?

Head first between the legs with one leg slightly further ahead than the other, in litter-bearing species, the fetus may present backwards or forwards without issue

What does stage 3: expulsion of fetal membranes entail about labor?

Inflammatory process, uterine contractions, chorionic villi loosen, expulsion of the placenta, delayed in ruminants due to cotyledons-caruncle separating independently, suckling → oxytocin → further contractions for placental release

What is dystocia?

Overarching term for a difficult labor

Why might a labor be difficult?

Abnormal presentation, excessive fetal size (most cases of dystocia in cattle), multiple births, etc.

What is the “red bag” in mares?

Premature separation of the chorioallantois from the uterus, deprives the fetus of oxygen, water fails to break

What is puerperium?

Physiological changes after birth, uterine involution, no/irregular estrous cycles

When is the critical period for pregnancy loss?

Fertilization and zygote genomic activation, embryonic failure, embryonic-induced luteal maintenance, implantation, placental development, parturition, disease (possible at all times)

When are most pregnancies lost?

Early on in the pregnancy (may not even know animal was pregnant)

What is early pregnancy loss commonly associated with?

Impaired conceptus signaling for luteal maintenance

What is late pregnancy loss commonly associated with?

Impaired implantation/placentation