You can still get your girlfriend/wife pregnant while on steroids but it is extremely unlikely. Staying on steroids year round (even just a TRT dosage) significantly increases your chance of infertility. If you plan on starting TRT (blasting and cruising) I would go to a sperm bank and donate a sample before doing so. You can have them freeze it for around $250/year.
In my opinion - Blasting and cruising is not a good idea unless you are adamant that you are done having kids and a doctor is prescribing the TRT cruise dosage for you. Being on steroids year round (even TRT) puts you at a hugely increased risk of prostate cancer. You want to work with your doctor so you can routinely get blood work done and ensure that you stay healthy.
A much healthier option is to do as follows:
1. Run your cycle.
2. After your cycle run a good pct protocol such as the perfect PCT:
http://www.evolutionary.org/the-perfect-post-cycle-therapy-pct/
3. After the PCT protocol, run a SARMS bridge - such as the SARMS triple stack:
http://www.evolutionary.org/the-SARMS-triple-stack-protocol
4. After the triple stack, run a mini PCT. 4 weeks of the following:
clomid at 25mg/day
nolvadex at 20mg/day
HCGenerate ES at 5 capsules/day
n2guard at 3 capsules/day
5. Then wait 3-4 weeks, ideally get blood work done to make sure everything is in the normal range and start your next cycle.
With doing 1-5 you will continue growing off cycle and your natural testosterone production won't be suppressed. It is a healthier route all around.
You can get everything you need off sarms1.com, n2bm.com and ag-guys.com