Physiology of Labor, Birth, and High-Risk Pre-Existing Conditions in Pregnancy

Vocabulary practice flashcards covering the normal physiology, stages, critical factors (5 P's), and fetal heart rate monitoring of labor and birth, as well as the identification, pathophysiology, and management of pre-existing cardiovascular, endocrine, and systemic maternal conditions during pregnancy.

Lightening

The descent of the fetal presenting part into the maternal pelvis, relieving fundal pressure on the diaphragm to make breathing easier, while simultaneously increasing pelvic pressure that leads to urinary frequency, lower extremity edema, and increased vaginal secretions.

Nesting

A sudden burst of energy experienced by the pregnant client prior to labor onset, characterized by intense cleaning and organization to prepare the home for the infant's arrival.

Braxton Hicks Contractions

Irregular, intermittent contractions felt as a tightening or pulling sensation in the front of the abdomen that typically decrease or resolve with walking, voiding, oral fluids, or position changes.

Cervical Ripening

The physiological process prior to labor during which the cervix undergoes softening, shortening, and thinning (effacement) in response to hormonal and mechanical factors.

Spontaneous Rupture of Membranes (SROM)

The natural rupture of the amniotic sac prior to or during labor, experienced by 1 in 4 pregnant individuals before labor begins, presenting as a sudden gush or a steady trickle of clear, straw-colored fluid.

Bloody Show

The expulsion of the cervical mucus plug accompanied by a small amount of pink-tinged or bloody mucus as the cervix begins to soften, efface, and dilate.

True Labor

Uterine contractions that occur at regular, increasing intervals, intensify over time, originate in the back and radiate to the front of the abdomen, increase with physical activity, are not halted by sedation or sleep, and produce progressive cervical effacement and dilation.

False Labor

Uterine contractions that are irregular, do not increase in intensity or frequency, remain localized to the lower abdomen and groin, decrease with walking, sedation, or rest, and do not cause progressive cervical changes.

First Stage of Labor

The period from the onset of regular uterine contractions with progressive cervical dilation until the cervix is fully dilated to $10\,cm$, encompassing an early phase ($0\text{--}5\,cm$) and an active phase ($6\text{--}10\,cm$).

Second Stage of Labor

The stage of labor extending from complete cervical dilation ($10\,cm$) to the birth of the neonate, divided into a latent phase (laboring down) and an active phase (pushing).

Third Stage of Labor

The period of labor spanning from the birth of the neonate to the complete delivery of the placenta and fetal membranes.

Fourth Stage of Labor

The initial maternal physiological recovery and stabilization period occurring $1\text{--}4\,hours$ immediately following birth.

Crowning

The point in the second stage of labor when the fetal head is encircled by the external opening of the vagina and no longer recedes between contractions, indicating that birth is imminent.

The 5 P's of Labor

The five critical factors that interact to govern the labor and birth process: Passenger (fetus and placenta), Passageway (birth canal and bony pelvis), Powers (physiologic forces of labor), Position (of the birthing client), and Psyche (psychosocial considerations and emotional readiness).

Powers

The primary involuntary physiological forces (uterine contractions that rhythmically tighten, shorten, and pull up the uterus to thin and dilate the cervix) and secondary voluntary forces (intra-abdominal pushing or bearing down) that drive fetal descent.

Fetal Attitude

The posture of the fetal body parts in relation to one another; the normal attitude is general flexion, which presents the smallest anteroposterior diameter of the fetal head to the maternal pelvis.

Fetal Lie

The relationship of the long axis (spine) of the fetus to the long axis (spine) of the pregnant client, categorized as longitudinal ($96\%\text{--}97\%$ cephalic/vertex, $3\%$ breech) or transverse ($<1\%$).

Fetal Presentation

The body part of the fetus that enters the maternal pelvic inlet first; categorized as cephalic (vertex, sinciput, brow, face), breech (frank, complete, footling), or shoulder.

Frank Breech Presentation

A breech presentation where the fetal hips are flexed and both knees and legs are fully extended upward toward the chest, resulting in the buttocks presenting to the maternal cervix first.

Fetal Station

The relationship of the lowest border of the presenting part to an imaginary line drawn between the maternal ischial spines, measured in centimeters from $-5\,cm$ (above spines) to $+5\,cm$ (below spines), with $0\,station$ representing the ischial spines.

Engagement

The mechanism whereby the largest diameter of the fetal presenting part descends into the maternal true pelvis to reach the level of the ischial spines, documented as $0\,station$.

Ballotable

A clinical term indicating that the fetal presenting part is freely movable above the maternal pelvic inlet and has not yet engaged.

Cardinal Movements of Labor

The sequence of positional adaptations made by the fetus as it descends through the birth canal: engagement, descent, flexion, internal rotation, extension, external rotation (restitution), and expulsion.

Effacement

The shortening and thinning of the cervical canal and drawing up of the internal os into the uterine side walls, progressing from fully uneffaced ($0\%$) to paper thin ($100\%$).

Pelvic Shapes

The four structural categories of the female bony pelvic inlet and cavity that impact the passageway: Gynecoid (round, optimal for vaginal birth), Android (heart-shaped), Anthropoid (oval-shaped), and Platypelloid (flat).

Leopold's Maneuvers

A systematic four-part abdominal palpation technique used by clinicians to assess the client's abdomen to evaluate fetal lie, presentation, position, and engagement.

Dystocia

An abnormal or uncoordinated labor pattern that can be indirectly triggered by severe psychological stress, where high anxiety stimulates the sympathetic nervous system to release catecholamines (epinephrine and norepinephrine), producing myometrial dysfunction.

Baseline Fetal Heart Rate

The average fetal heart rate rounded to increments of $5\,bpm$ evaluated over a $10\text{-minute}$ window, excluding accelerations, decelerations, and periods of marked variability; normal baseline is $110\text{--}160\,bpm$.

Fetal Tachycardia

A sustained baseline fetal heart rate greater than $160\,bpm$ lasting for $10\,minutes$ or longer.

Fetal Bradycardia

A sustained baseline fetal heart rate lower than $110\,bpm$ lasting for $10\,minutes$ or longer.

Baseline FHR Variability

Irregular fluctuations in the baseline fetal heart rate of two cycles per minute or greater, quantified visually as the amplitude range from the peak to the trough.

Moderate Variability

Fluctuations in the baseline fetal heart rate with an amplitude range of $6\text{--}25\,bpm$, indicating adequate fetal oxygenation, normal central nervous system function, and reliably predicting the absence of hypoxic injury at the time of observation.

FHR Acceleration

An abrupt baseline increase in fetal heart rate of at least $15\,bpm$ lasting at least $15\,seconds$ ($10\times 10$ if gestation is $<32\,weeks$), serving as a primary indicator of fetal movement and neurological well-being.

Early Deceleration

A visually apparent, symmetric, gradual decrease in fetal heart rate that inversely mirrors the uterine contraction, reaching its nadir at the contraction acme; caused by a benign vagal reflex from fetal head compression.

Variable Deceleration

An abrupt, visually apparent decrease in fetal heart rate below baseline ($\ge 15\,bpm$ lasting $\ge 15\,seconds$ and $<2\,minutes$) with an unpredictable shape and variable timing relative to contractions, caused by umbilical cord compression.

Late Deceleration

A visually apparent, symmetric, gradual decrease in fetal heart rate that begins after the onset of a contraction, reaches its nadir after the contraction peak, and returns to baseline only after the contraction ends, resulting from uteroplacental insufficiency.

Chronic Hypertension in Pregnancy

Blood pressure exceeding $140/90\,mmHg$ diagnosed prior to conception or before $20\,weeks$ of gestation; managed with nutrition, low-dose aspirin starting in the second trimester, and antihypertensives such as Labetalol or Nifedipine (avoiding ACE inhibitors and ARBs).

Peripartum Cardiomyopathy

A nonischemic left ventricular systolic dysfunction leading to heart failure that develops in the final month of pregnancy or within several months postpartum, occurring in $25\text{--}100\,per\,100,000$ live births and disproportionately affecting non-Hispanic Black individuals, advanced maternal age, multifetal gestations, and hypertensive states.

NYHA Class I Cardiac Disease

A cardiac disease classification where the client experiences no limitation of physical activity, ordinary activity causes no undue fatigue, palpitations, dyspnea, or anginal pain, and there is no increased risk of maternal mortality.

NYHA Class IV Cardiac Disease

A severe cardiac classification where any physical activity produces discomfort, symptoms of cardiac insufficiency or angina are present even at rest, and pregnancy carries an extremely high risk of maternal morbidity and mortality.

Pregestational Diabetes Mellitus

Diabetes mellitus (Type 1 absolute insulin deficiency or Type 2 insulin resistance) existing prior to pregnancy, requiring preconception glycemic control ($HbA1c < 6.5\%$) to prevent congenital anomalies and antepartal monitoring ($HbA1c < 6\%$ every 2 months).

Changing Insulin Needs in Pregnancy

The physiological pattern of insulin requirements across gestation: reduced in the first trimester due to nausea and increased peripheral sensitivity, followed by a double to quadruple rise in the second and third trimesters from placental anti-insulin hormones, followed by a sharp precipitous drop at birth upon placental delivery.

Macrosomia

Excessive intrauterine fetal growth (large for gestational age) commonly resulting from maternal hyperglycemia crossing the placenta, which stimulates fetal pancreatic beta cells to produce excess fetal insulin acting as a powerful growth hormone.

Neonatal Abstinence Syndrome (NAS)

A constellation of physiological and behavioral withdrawal manifestations exhibited by a neonate after birth following intrauterine exposure to addictive substances, most prominently opioids and benzodiazepines.

Sickle Cell Vaso-Occlusive Crisis

Painful microvascular occlusions caused by sickled erythrocytes during pregnancy that compromise maternal tissue perfusion and can interrupt oxygen delivery to the fetus, posing high risks for spontaneous abortions, preterm labor, and intrauterine growth restriction.

Trauma-Informed Care

A compassionate model of care recommended for vulnerable pregnant individuals, including victims of sexual violence, built upon the four pillars: Realize the widespread impact of trauma, Recognize signs and symptoms, Respond by integrating knowledge into practice, and actively resist Re-traumatization.