Endometriotic tissue that implants on the pleural surface can bleed in response to the hormonal changes of the menstrual cycle, causing what is known as a catamenial hemothorax as part of thoracic endometriosis along with catamenial pneumothorax, catamenial hemoptysis, and lung nodules of endometriosis. Catamenial hemothorax represents 14% of cases of thoracic endometriosis syndrome while catamenial pneumothorax is seen in 73%, catamenial hemoptysis in 7%, and pulmonary nodules in 6%. Mechanism
When a hemothorax occurs, blood enters the pleural cavity. The blood loss from the circulation has several effects. Firstly, as blood builds up within the pleural cavity, it begins to interfere with the normal movement of the lungs, preventing one or both lungs from fully expanding and thereby interfering with the normal transfer of oxygen and carbon dioxide to and from the blood. Secondly, blood that has been lost into the pleural cavity can no longer be circulated. Hemothoraces can lead to significant blood loss – each half of the thorax can hold more than 1500 milliliters of blood, representing more than 25% of an average adults total blood volume. The body may struggle to cope with this blood loss, and tries to compensate by maintaining blood pressure by forcing the heart to pump harder and faster, and by squeezing or constricting small blood vessels in the arms and legs. These compensatory mechanisms can be recognised by a rapid resting heart rate and cool fingers and toes.If the blood within the pleural cavity is not removed, it will eventually clot.
Neonatal hypocalcemia is an abnormal clinical and laboratory hypocalcemia condition that is frequently observed in infants. It is commonly presented within the first 72 hours of a newborns life.Healthy term infants go through a physiological nadir of serum calcium levels at 7.5 - 8.5 mg/dL by day 2 of life. Hypocalcemia is a low blood calcium level. A total serum calcium of less than 8 mg/dL (2mmol/L) or ionized calcium less than 1.2 mmol/L in term neonates is defined as hypocalcemia. In preterm infants, it is defined as less than 7mg/dL (1.75 mmol/L) total serum calcium or less than 4mg/dL (1 mmol/L) ionized calcium. Both early onset hypocalcemia (presents within 72h of birth) and late onset hypocalcemia (presents in 3-7 days after birth) require calcium supplementation treatment. Infants with intrauterine growth retardation, perinatal asphyxia, preterm, and diabetic mothers are most likely to develop neonatal hypocalcemia. It is not understood why premature infants have hypocalcemia, but a proposed idea is that a large increase of calcitonin may lead to hypocalcemia. Another hypothesis includes impaired secretion of PTH or Parathyroid hormone. Cause
Risk factors of early neonatal hypocalcemia 

Prematurity
Perinatal asphyxia
Diabetes mellitus in the mother
Maternal hyperparathyroidism
Intrauterine growth retardation (IUGR)
Iatrogenic

Risk factors
Risk factors of late neonatal hypocalcemia

Exogenous phosphate load
Use of gentamicin
Gender and ethnic: late neonatal hypocalcemia occurred more often in male infants and Hispanic infants
OthersMagnesium deficiency
Transient hypoparathyroidism of newborn
Hypoparathyroidism due to other causes (DiGeorge Syndrome)

References

Jain, A., Agarwal, R., Sankar, M. J., Deorari, A., & Paul, V. K. (2010). Hypocalcemia in the newborn. Indian Journal of Pediatrics, 77, 1123-1128.