The incidence of hydatidiform mole is expressed as molar gestations per number of pregnancies. In the US, molar pregnancy (MP) is identified in 1 in 1000 to 1200 pregnancies, and in 1 in 600 therapeutic abortions.[5]Altieri A, Franceschi S, Ferlay J, et al. Epidemiology and aetiology of gestational trophoblastic diseases. Lancet Oncol. 2003 Nov;4(11):670-8.
http://www.ncbi.nlm.nih.gov/pubmed/14602247?tool=bestpractice.com
The incidence seems to be higher in Latin American and Asian countries, although the etiological factors involved have not yet been determined.[5]Altieri A, Franceschi S, Ferlay J, et al. Epidemiology and aetiology of gestational trophoblastic diseases. Lancet Oncol. 2003 Nov;4(11):670-8.
http://www.ncbi.nlm.nih.gov/pubmed/14602247?tool=bestpractice.com
[6]Kim SJ, Bae SN, Kim JH, et al. Epidemiology and time trends of gestational trophoblastic disease in Korea. Int J Gynaecol Obstet. 1998 Apr;60 Suppl 1:S33-8.
http://www.ncbi.nlm.nih.gov/pubmed/29645254?tool=bestpractice.com
[7]Braga A, Uberti EM, Fajardo Mdo C, et al. Epidemiological report on the treatment of patients with gestational trophoblastic disease in 10 Brazilian referral centers: results after 12 years since International FIGO 2000 Consensus. J Reprod Med. 2014 May-Jun;59(5-6):241-7.
http://www.ncbi.nlm.nih.gov/pubmed/24937964?tool=bestpractice.com
Women with a previous diagnosis of hydatidiform mole have a 1% to 2% chance of molar gestation in subsequent pregnancies.[8]Sebire NJ, Fisher RA, Foskett M, et al. Risk of recurrent hydatidiform mole and subsequent pregnancy outcome following complete or partial hydatidiform molar pregnancy. BJOG. 2003 Jan;110(1):22-6.
http://www.ncbi.nlm.nih.gov/pubmed/12504931?tool=bestpractice.com
[9]Vargas R, Barroilhet LM, Esselen K, et al. Subsequent pregnancy outcomes after complete and partial molar pregnancy, recurrent molar pregnancy, and gestational trophoblastic neoplasia: an update from the New England Trophoblastic Disease Center. J Reprod Med. 2014 May-Jun;59(5-6):188-94.
http://www.ncbi.nlm.nih.gov/pubmed/24937955?tool=bestpractice.com
There is a modestly increased incidence of MP among women less than 20 years of age, but women over 35 years of age have a significantly higher risk of MP, which increases progressively as maternal age advances.[10]Altman AD, Bentley B, Murray S, et al. Maternal age-related rates of gestational trophoblastic disease. Obstet Gynecol. 2008 Aug;112(2 Pt 1):244-50.
http://www.ncbi.nlm.nih.gov/pubmed/18669718?tool=bestpractice.com
[11]Savage PM, Sita-Lumsden A, Dickson S, et al. The relationship of maternal age to molar pregnancy incidence, risks for chemotherapy and subsequent pregnancy outcome. J Obstet Gynaecol. 2013 May;33(4):406-11.
https://www.tandfonline.com/doi/abs/10.3109/01443615.2013.771159
http://www.ncbi.nlm.nih.gov/pubmed/23654327?tool=bestpractice.com
[12]Gockley AA, Melamed A, Joseph NT, et al. The effect of adolescence and advanced maternal age on the incidence of complete and partial molar pregnancy. Gynecol Oncol. 2016 Mar;140(3):470-3.
http://www.ncbi.nlm.nih.gov/pubmed/26777992?tool=bestpractice.com
[13]Di Cintio E, Parazzini F, Rosa C, et al. The epidemiology of gestational trophoblastic disease. Gen Diagn Pathol. 1997 Nov;143(2-3):103-8.
http://www.ncbi.nlm.nih.gov/pubmed/9443567?tool=bestpractice.com
[14]Braga A, Growdon WB, Bernstein M, et al. Molar pregnancy in adolescents. J Reprod Med. 2012 May-Jun;57(5-6):225-30.
http://www.ncbi.nlm.nih.gov/pubmed/22696817?tool=bestpractice.com
[15]Soares RR, Maestá I, Colón J, et al. Complete molar pregnancy in adolescents from North and South America: Clinical presentation and risk of gestational trophoblastic neoplasia. Gynecol Oncol. 2016 Sep;142(3):496-500.
http://www.ncbi.nlm.nih.gov/pubmed/27423380?tool=bestpractice.com
Despite these findings, most molar pregnancies occur in women between 20 and 30 years of age because there is a larger total number of pregnancies in this age group.