MARIJUANA - PREGNANCY & BREASTFEEDING
Marijuana use by mothers while pregnant (prenatal) has been linked with:
Fetal growth and neurodevelopmental impairment
Low birth rate
Greater risk of stillbirth
Increased risk for miscarriage
Altered responses to visual stimuli, increased trembling, and a high-pitched cry
Detrimental effects on foetal development. 
As prenatally exposed children age, they may experience:
Developmental and hyperactivity disorders
Gaps in problem-solving skills, memory, and the ability to remain attentive.
Decreased motor development at 1 year of age
Childhood attention problems and lower scores on problem-solving measures
Increased likelihood of marijuana use as a young adult even when other factors that influence drug use are considered.
Moderate concentrations of THC used by mothers after delivery (postnatal) can:
Find its way into breast milk potentially affecting the quality and quantity of milk produced
Affect brain development
Have long-lasting effects on the child, including increasing stress responsivity and abnormal patterns of social interactions.
Breathing second-hand marijuana smoke may also increase the chances for developmental problems in the baby. 
Reproductive toxicity in early gestation has been found to affect spermatogenesis, which is the process of the formation of male gamete including meiosis and formation of sperm cells.
 Volkow ND, Compton WM, Wargo EM. The risks of marijuana use during pregnancy. JAMA. 2017;317(2):129-130. See the studies below.
 Trends in Self-reported and Biochemically Tested Marijuana Use Among Pregnant Females in California From 2009-2016; http://cdn.cnn.com/cnn/2017/images/12/22/pot.during.pregnancy.jld170046.pdf
Brown QL, Sarvet AL, Shmulewitz D, Martins SS, Wall MM, Hasin DS. Trends in marijuana use among pregnant and nonpregnant reproductive-aged women,2002-2014.JAMA. 2017;317(2):207-209.
Salas -Wright CP, Vaughn MG, Ugalde J, Todic J. Substance use and teen pregnancy in the United States. Addict Behav. 2015;45:218-225.
Volkow ND, Compton WM, Wargo EM. The risks of marijuana use during pregnancy. JAMA. 2017;317(2):129-130.
Ko JY, Farr SL, Tong VT, Creanga AA, Callaghan WM. Prevalence and patterns of marijuana use among pregnant and nonpregnant women of reproductive age. Am J Obstet Gynecol. 2015;213(2):201.e1-201.e10.
ElSohly MA, Mehmedic Z, Foster S, Gon C, Chandra S, Church JC. Changes in cannabis potency over the last 2 decades (1995-2014). Biol Psychiatry. 2016; 79(7):613-619.
The American Medical Association has warned marijuana use may be linked with low birth weight, premature birth, behavioral and other problems in young children.