LOL need a sticky with all of the abbreviations we use in here! Here are some of the most common ones that I have found while being on forums:
2WW - 2 week wait (but who doesn't know this one?!)
AF - Aunt Flo of course!
ATM - At The Moment
BB's - Boobs
BBT - Basal Body Temperature
BC - Birth Control (lowercase can mean because)
BD - Baby Dance
BFN/BFP - Big Fat Negative or Big Fat Positive
BMS - Baby Making Sex
CB - Cycle Buddy
CD - Cycle Day
CM - Cervical Mucus
DPO - Days Past Ovulation
DTD - Do The Deed
Dx - Diagnosis
EDD - Estimated Due Date
EWCM - Egg White Cervical Mucus
FMU - First Morning Urine
FRER - First Response Early Result Home Pregnancy Test
FTM - First Time Mom
FWIW - For What It's Worth
FX - Fingers Crossed
FYI - For Your Information
HPT - Home Pregnancy Test
HTH - Hope This Helps
IDK - I Don't Know
IF - Infertility
IMHO - In My Humble (or Honest) Opinion
IUI - Intrauterine Insemination
IVF - In vitro fertilization
L&D - Labor and Delivery
LMP - Last Monthly Period
LP - Luteal Phase
MC - Miscarriage
NTNP - Not Trying Not Preventing
O - Ovulation
O'd - Ovulated
OPK - Ovulation Predictor Kit
OT - Off Topic
PCOS - Polycystic Ovarian Syndrome
PG - Pregnant
POAS - Pee On A Stick
POS - Positive
RE - Reproductive Endocrinologist
SMEP - Sperm Meets Egg Plan
TYIA - Thank You In Advance
US - Ultrasound
WTO - Waiting to Ovulate

HTH!