***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE To assess the association between recent cigarette smoking ( CS ) in female and male partners and assisted reproduction technology ( ART ) outcomes . DESIGN Cohort prospect i ve study . SETTING University ART program in Chile . PATIENT(S ) One hundred sixty-six couples seeking pregnancy through ART . INTERVENTION(S ) Follicular fluid ( FF ) and serum cotinine concentrations were measured in female partners .  Self-reported CS data were collected through personal interviews . MAIN OUTCOME MEASURE(S ) The association between female recent smoking , assessed by FF and serum cotinine concentrations , and ART outcomes , such as number of ova retrieved and implantation rates , and the association between self-reported male recent smoking and live birth rates . RESULT ( S ) A significant age-adjusted association between increased FF cotinine level and decreased number of ova retrieved was found . The male partner 's smoking habit significantly decreased the live birth rate from 21.1 % to 7.8 % . Serum cotinine concentrations paralleled those of FF . CONCLUSION ( S ) The hypothesis of a detrimental effect of recent female smoking over implantation rates is rejected . However , recent male smoking is associated with significantly decreased live birth rates even after adjusting for confounders . Female recent smoking was significantly associated with decreased number of retrieved ova Several studies published within the past 10 years indicate that smoking reduces fecundity , but not all studies have found this effect , and smoking cessation is not used routinely in infertility treatment in Europe . The present study was design ed to examine  male and female smoking at the start of a couple 's waiting time to a planned pregnancy . Two types of sample s were used : population -based sample s of women aged 25 - 44 years who were r and omly selected in different countries from census registers and electoral rolls , in which the unit of analysis was the couple ; and pregnancy-based sample s of pregnant women ( at least 20 weeks ' pregnant ) who were consecutively recruited during prenatal care visits , in which the unit of analysis was a pregnancy . More than 4,000 couples were included in each sample , and 10 different regions in Europe took part in data collection . The data were collected between August 1991 and February 1993 by personal interview in all population -based sample s and in all but three regions of the pregnancy sample , where self-administered question naires were used . The results based on the population sample showed a remarkably coherent association between female smoking and subfecundity in each individual country and in all countries together , both with the first pregnancy ( odds ratio ( OR ) = 1.7 , 95 % confidence interval ( CI ) 1.3 - 2.1 , at the upper level of exposure ) and during the most recent waiting time to pregnancy ( OR = 1.6 , 95 % CI 1.3 - 2.1 ) . Results based on the pregnancy sample were similar ( OR = 1.7 , 95 % CI 1.3 - 2.3 ) . No significant association was found with male smoking ( in the population sample , OR = 0.9 , 95 % CI 0.7 - 1.1 ( first pregnancy ) and OR = 1.0 , 95 % CI 0.9 - 1.3 ( most recent waiting time ) ; in the pregnancy sample , OR = 0.9 , 95 % CI 0.7 - 1.1 ) . The fecundity distribution among smokers appeared to be shifted toward longer waiting times without a change in the shape of the distribution . Women who have difficulty conceiving should try to stop smoking or to reduce their smoking to less than 10 cigarettes per day The electromechanical activity of the uterus was studied in 18 healthy women ( mean age 38.3+/-14.2 SD years ; 8 were nulliparous , 10 multiparous ) aim ing at characterizing a normal electrohysterogram . Two monopolar silver-silver chloride electrodes were applied to the uterine and one to the cervical mucosa . The uterine pressure was measured by a water-perfused tube connected to a pressure transducer . Monophasic , negatively deflected slow waves or pacesetter potentials ( PPs ) were recorded from the 2 uterine electrodes . They had regular rhythm and exhibited the same frequency , amplitude and velocity of conduction by the 2 electrodes . The PPs were followed r and omly by bursts of action potentials ( APs ) . The APs and not the PPs were associated with uterine pressure rise . PPs from the cervix were registered only occasionally . The occurrence of the electric activity is believed to depend on the smooth muscle fibers content which is high in the uterine body and meagre in the cervix . The APs seem to have contractile activity which might act to sweep away the uterine secretions . According to the uterocervical reflex , the cervix dilates upon uterine contractions . A normal electrohysterogram could be characterized . It might show a different pattern in the various uterine pathologic conditions and may thus represent an investigative tool in the diagnosis of such disorders OBJECTIVE To evaluate the predictive value of serial uterine artery Doppler ultrasound for embryo implantation in in-vitro fertilization (IVF)-intracytoplasmic sperm injection ( ICSI ) cycles . METHODS This was a prospect i ve observational study at the VU University Medical Center , Amsterdam . Patients with an indication for IVF or IVF-ICSI according to departmental protocol underwent controlled ovarian hyperstimulation followed by IVF or IVF-ICSI and embryo transfer and had serial Doppler ultrasound performed during this treatment cycle . Patient and cycle characteristics , number of conceptions and ongoing pregnancies and pulsatility index ( PI ) of both uterine arteries on different cycle days were assessed and results were compared between patients who conceived and those who did not . RESULTS Of the 102 patients enrolled into the study , 83 underwent embryo transfer . Of these , 41 became pregnant and 42 did not ( Group 1 ) . Of the 41 pregnancies , 30 were ongoing ( Group 2 ) and 11 miscarried ( Group 3 ) . Between Groups 1 , 2 and 3 , linear regression revealed no significant difference between any of the variables examined except in the quality of transferred embryos . There was no significant difference in the mean PI of the left and right uterine arteries on any day of the cycle , or in the change in PI during the cycle . Receiver-operating characteristics curves derived to determine the performance of PI to predict pregnancy outcome supported our findings that the uterine artery PI is not a suitable marker for identifying patients with implantation failure . Multivariate analysis showed no relationship between pregnancy and PI between groups , but it did show a relationship between pregnancy and some patient and cycle characteristics . CONCLUSION In an unselected group of patients undergoing IVF or IVF-ICSI and embryo transfer , serial Doppler ultrasound examination of the uterine artery does not discriminate between cycles result ing in ongoing pregnancy , miscarriage and no pregnancy The authors earlier conducted a retrospective study of time to pregnancy among a group of pregnant women in Minnesota , in order to investigate the relation between cigarette smoking and fecundability . Further analysis of these data shows that women who had been exposed as children to cigarette smokers had increased fertility . This finding lacks biologic plausibility . However , the authors found a similar association in a group of North Carolina women whose fecundability had been measured prospect ively . Furthermore , both groups showed an apparent dose-response effect . The authors briefly describe this unexpected finding so that it might be more fully explored in other studies OBJECTIVE To study acute hemodynamic alterations in the fetal-placental maternal system immediately after maternal exposure to nicotine . METHODS This is a noncontrolled experimental study involving 21 pregnant smoking women , r and omly selected , with uncomplicated pregnancies and without risk factors for fetal heart disease . Patients underwent ultrasound and fetal echocardiography before and after smoking a cigarette . They were asked to abstain from smoking for 12 hours before the study . The mean nicotine content of the cigarettes used in the study was 0.5 mg of nicotine and 6 mg of carbon monoxide . RESULTS The average number of cigarettes smoked per a day prior to the study was 9.67 . Gestational age ranged between 18 and 36 weeks . The mean maternal heart rate was elevated ( P<0.001 ) as was the mean fetal heart rate ( P=0.044 ) . Maternal systolic blood pressure ( P=0.004 ) and diastolic blood pressure ( P=0.033 ) were also elevated after smoking . A decrease occurred in the systolic/diastolic ratio in the right uterine artery ( P=0.014 ) and in the left uterine artery ( P=0.039 ) . The other hemodynamic variables remained unchanged . CONCLUSION Cigarette smoking can cause changes in physiologic variables of fetal-placental circulation , but it does not change fetal cardiac function , in the dose of nicotine and its components used in this study . The decrease in systolic/diastolic ratio in the uterine arteries is probably related to a dose-dependent nicotine pattern BACKGROUND Smoking has been reported to promote infertility . The zona pellucida plays an important role in fertilization and implantation . We report , for the first time , the effect of cigarette smoking on zona pellucida thickness of oocytes and embryos as one of the factors that may interfere with fertility . METHODS This study comprised 169 women , grouped according to their smoking habits : 31 active smokers , whose husb and s do not smoke ; 44 active smokers , whose husb and s smoke ; 65 passive smokers , because of smoking husb and s and 29 non-smokers ( women and husb and s ) .  Zona pellucida thickness was measured prospect ively on printed photos of 903 oocytes and 456 embryos . RESULTS The zona pellucida thickness of oocytes and embryos of non-smoking women was significantly thinner than those of active and passive smokers . However , no significant differences were observed in the natural ability of the zona pellucida to become thinner after 48 h in culture . CONCLUSIONS Our study demonstrates that active and passive cigarette smoking increases the zona pellucida thickness of oocytes and embryos . Our findings also show that active and passive smoking has no significant effect on the thinning mechanism of the zona pellucida , which implies that it is independent of the initial zona pellucida thickness Objectives The ratio of trans-3′hydroxycotinine/cotinine ( 3HC/COT ) is a marker of CYP2A6 activity , an important determinant of nicotine metabolism . This analysis sought to conduct a combined genetic epidemiologic and pharmacogenetic investigation of the 3HC/COT ratio in plasma and urine . Methods One hundred and thirty-nine twin pairs [ 110 monozygotic and 29 dizygotic ] underwent a 30-min infusion of stable isotope-labelled nicotine and its major metabolite , cotinine , followed by an 8-h in-hospital stay .  Blood and urine sample s were taken at regular intervals for analysis of nicotine , cotinine , and metabolites . DNA was genotyped to confirm zygosity and for variation in the gene for the primary nicotine metabolic enzyme , CYP2A6 ( variants genotyped : * 1B , * 1 × 2 , * 2 , * 4 , * 9 , * 12 ) . Univariate biometric analyses quantified genetic and environmental influences on each measure in the presence and absence of covariates , including measured CYP2A6 genotype . Results There was a substantial amount of variation in the free 3HC/COT ratio in plasma ( 6 h postinfusion ) attributable to additive genetic influences ( 67.4 % , 95 % confidence interval=55.9–76.2 % ) . The heritability estimate was reduced to 61.0 and 49.4 % , respectively , after taking into account the effect of covariates and CYP2A6 genotype . In urine ( collected over 8 h ) , the estimated amount of variation in the 3HC/COT ratio attributable to additive genetic influences was smaller ( 47.2 % , 95 % confidence interval=0–67.2 % ) and decreased to 44.6 and 42.0 % after accounting for covariates and genotype . Conclusion Additive genetic factors are prominent in determining variation in plasma 3HC/COT but less so in determining variation in urine 3HC/COT In the present study we investigated the effect of a woman 's smoking status on the quality of the oocyte , zygote , and on day 3 pre-embryo , as well as the likelihood of achieving an ongoing pregnancy at 8 weeks . Smokers presented a higher number of nonfertilized oocytes than nonsmokers ( 20.1 % vs. 10.8 % of fertilization failure ) , by comparable clinical pregnancy rate for smokers ( 40.8 % ; 28/72 ) and for nonsmokers ( 39.2 % ; 23/58 ) OBJECTIVE To search for a possible correlation between an effective marker of smoking and uterine and placental resistance during pregnancy . STUDY DESIGN A prospect i ve study was conducted at the Intercommunal Hospital Center of Montreuil , France : 81 healthy pregnant women underwent uterine and placental Doppler and cotidin blood assay  , the 
    Output:
    
The effects of cigarette smoke are dose-dependent and are influenced by the presence of other toxic substances and hormonal status .
Individual sensitivity , dose , time and type of exposure also play a role in the impact of smoke constituents on human fertility .
All stages of reproductive functions are targets of cigarette smoke toxicants .