title: [Frequency of multiple pregnancy].
abstract: OBJECTIVE
  The aim of this research was to find out the frequency and tendency of multiple pregnancy. Study design. There are used retrospective and prospective comparative analysis. The study includes 51162 births, 960 twins, 39 triplets and 1 quadruplets.
  
  
  RESULTS
  The number of multiple pregnancy in 1994 was 44, but in 2009 it was 152. The frequency of twins increased from 1.18% in the beginning of the observed period to 3.62% in the end of the period. The frequency of triplets chanced from 0.06% to 0.34%. We determined that the number of twins increased 3 times and the number of triplets - 6 times. In the beginning of the researched period in 2005, the frequency of twin pregnancy shows a tendency of smooth increase, while form 2006 there is a significant and rapid increase. The frequency of the triplet's births shows relative stability from 1996 till 2006, while from 2007 till now there is a progressive increase in it too.
  
  
  CONCLUSIONS
  There is a significant increase in the frequency of the multiple preganancies, observed in twins as well as in triplets. There is a stable tendency of increasing, which has the following characteristics smooth growth in the beginning of the period and rapid expand in the last years. The problem of the increasing frequency of the multiple pregnancies and the following up complications must be the aim of our future research and discussion.
authors.forename: A
authors.initials: A
authors.lastname: Nikolov
authors.forename: I
authors.initials: I
authors.lastname: Petrova
authors.forename: S
authors.initials: S
authors.lastname: Nashar
authors.forename: P
authors.initials: P
authors.lastname: Markov
mesh_terms: D002031:Bulgaria; D005260:Female; D006801:Humans; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D012189:Retrospective Studies; D014310:Triplets; D014427:Twins