AUTHOR=Pennoni Fulvia , Barbato Michele , Del Zoppo Serena 

TITLE=A Latent Markov Model with Covariates to Study Unobserved Heterogeneity among Fertility Patterns of Couples Employing Natural Family Planning Methods

JOURNAL=Frontiers in Public Health

VOLUME=Volume 5 - 2017

YEAR=2017

URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2017.00186

DOI=10.3389/fpubh.2017.00186

ISSN=2296-2565

ABSTRACT=Purpose:
We use the  historical data from European Study of Daily Fecundability and we develop an algorithm to 
determine the fertile window in a  woman's cycle  according to the rules of the C.A.Me.N. symptothermal method proposed by the Centro Ambrosiano Metodi Naturali.
Our aim is to identify variables  acting on the probability of conception by considering the fertile window  
and  factors that cannot be explained by employing the observed covariates of individuals and couples.

 Methods:
We adopt the latent Markov model with covariates tailored for data collected at times when 
a latent process detects the dependence across fertile periods of each woman's cycle.
We consider measurement errors, transitions between pregnancy and non-pregnancy, 
and the prediction of conception rate over the fertile windows.  


Conclusions:
We find that the conception pattern is mainly related to  sexual intercourse behaviour during 
the fertile window and to previous pregnancies.  For the cohort under study,
we predict  a decline in the average conception rate across fertile windows.