Here is a list. Couldn't find the one I was describing.
______
TTC: Trying to conceive
2WW: Two-week wait (until you can take a pregnancy test)
AF: Aunt Flo(w), your period
BBT: Basal body temperature
BD: Baby dance, sex
BFN: Big fat negative (test result)
BFP: Big fat positive (test result)
CD: Cycle day
CM: Cervical mucus
DPO: Days past ovulation
EW: Eggwhite (re: consistency of cervical mucus)
EWCM: Eggwhite cervical mucus (ovulatory mucus)
FMU: First morning urine
hCG: Human chorionic gonadotropin (pregnancy hormone)
HPT: Home pregnancy test
IUI: Intrauterine Insemination
IVF: In Vitro Fertilization
LH: Luteinizing hormone
LMP: Last menstrual period
LP: Luteal phase
O: Ovulation
OPK: Ovulation predictor kit
PCOS (POS): Polycystic ovarian syndrome
PG: Pregnancy, pregnant
S/A: Sperm/semen analysis
I believe that if you scroll way, way down to the right, one of the Health Pages on MedHelp has some of the abbreviations that are used when ttc (trying to conceive), including bd (baby dance) for sex, af (Aunt Flo) for the period, and dh (dear husband), dd (dear daughter) and ds (dear son). Don't know if it is an exhaustive list, but last time I looked for it, it was there.