Ukungabi nenzalo ukwehluleka komuntu, isilwane noma isitshalo ukuzala ngezindlela zemvelo.Kuvamise hhayi isimo engokwemvelo umuntu omdala onempilo enhle, ngaphandle ephawuleka phakathi ezithile eusocial zinhlobo (ikakhulukazi haplodiploid izinambuzane). Kodwa-ke yisimo esinempilo sengane yomuntu noma enye inzalo encane, ngoba abakakutholi ukuthomba, isiqalo somzimba samandla okuzala . Enye incazelo yokungazali okuvame ukusetshenziswa kakhulu e-United States ngochwepheshe be-endocrinologists bokuzala, odokotela abasebenza ngokungabi nenzalo, ukubheka imibhangqwana efanelekile ukwelashwa yile: owesifazane ongaphansi kweminyaka engama-35 akakhulelanga ngemuva kwezinyanga eziyi-12 zokuya ocansini ngaphandle kokukhulelwa. Izinyanga eziyishumi nambili umkhawulo ophansi wesethenjwa we- Time to Pregnancy (TTP) yi-World Health Organisation. owesifazane ongaphezu kweminyaka engama-35 akakaze akhulelwe ngemuva kwezinyanga eziyisithupha zokuya ocansini ngaphandle kokukhulelwa. Lezi zikhathi zingabonakala ziguqulwa; lena yindawo lapho inqubomgomo yomphakathi ishaya khona isayensi.Umqondo ngukuthi kwabesifazane abangaphezu kweminyaka yobudala engama-35, njalo ngenyanga kubalwa futhi uma kwenziwa ukulinda ezinye izinyanga eziyisithupha ukufakazela isidingo sokungenelela kwezokwelapha, inkinga ingaba yimbi kakhulu.Okuhambisana nalokhu ukuthi, ngencazelo, ukwehluleka ukukhulelwa kwabesifazane abangaphansi kweminyaka engama-35 akubhekwa ngokuphuthuma okufanayo nakulabo abangaphezu kweminyaka engama-35. E-UK, imihlahlandlela yangaphambilini ye-NICE ichaze ukungazali njengokuhluleka ukukhulelwa ngemuva kocansi olungavikelekile iminyaka emibili lapho kungekho khona i-pathology yokuzala eyaziwayo.