Defendant appeals from a conviction for a third offense of driving while under the *437influence of an alcoholic beverage. Defendant pleaded guilty to a part I information charging her with DWI but pleaded not guilty to a part II information charging that the offense was a third DWI offense. The state and the defendant stipulated to the facts of the first and second offenses and the court entered a judgment of guilty on the third DWI offense. Defendant was sentenced to two years in the penitentiary. We affirm.
The first offense and arrest occurred on August 12, 1977. Defendant was convicted of that offense on December 15, 1977. Defendant’s second DWI conviction occurred on September 2, 1981. The date of the occurrence of the second offense does not appear in the record. The alleged third offense occurred on August 18, 1981, to which defendant entered a plea of guilty on a part I information on April 15, 1982.
We have been asked to interpret SDCL 32-23-4.1 which states: “No previous conviction for, or plea of guilty to, an offense under §§ 32-23-2 to 32-23-4, inclusive, occurring more than four years prior to the date of the violation being charged shall be used to determine that the violation being charged is a second, third or subsequent offense.” * The question is whether the four year period prior to the date of the most recent violation must include the date of prior offenses or the date of conviction on such offenses to determine if the most recent violation is a second, third, or subsequent offense.
A presumption of innocence exists before a defendant is convicted. This presumption cannot be used to enhance any penalty. Therefore, only convictions occurring on a date within the four years prior to the most recent offense are to be used in determining whether the most recent violation is a second or third offense. This is consistent with our prior interpretations that it is the previous DWI conviction or plea of guilty which affects enhancement. See State v. Dassinger, 294 N.W.2d 926 (S.D.1980); State v. Bacon, 286 N.W.2d 331 (S.D.1979).
Defendant’s most recent offense, which she pleaded guilty to, occurred on August 18, 1981. The four years prior to this offense included a conviction on December 15, 1977. The conviction for the second offense occurred on September 2, 1981, which was after the occurrence of the most recent offense. On April 15, 1982, when defendant pleaded guilty to the most recent offense, she had been convicted a second time on September 2, 1981. The September 2, 1981, conviction may be included as a second offense because SDCL 32-23-4.1 is a limitations statute designed to preclude the use of state convictions occurring four years prior to the date of the most recent offense. This enhancement statute imposes no restriction on the use of convictions or pleas occurring after the most recent offense but before the plea or conviction on the most recent offense. Cf. Perdue v. State, 341 N.W.2d 382 (S.D.1984); State v. Layton, 337 N.W.2d 809 (S.D.1983). Therefore, the circuit court correctly found defendant guilty of a third offense DWI as alleged in the part II information.
We also reject defendant’s contention that SDCL 32-23-4.1 violates the equal protection clause of the Fourteenth Amendment of the United States Constitution. To classify persons who may have committed prior DWI offenses on the basis of whether they are convicted of DWI offenses or are only alleged to have committed an offense is hardly arbitrary, irrational, or without some legitimate legislative purpose. See Railway Express Agency v. New York, 336 U.S. 106, 69 S.Ct. 463, 93 L.Ed. 533 (1949); City of Aberdeen v. Meidinger, 89 S.D. 412, 233 N.W.2d 331 (1975).
*438The circuit court’s judgment of conviction is affirmed.
POSHEIM, C.J., and DUNN, J., concur. WOLLMAN and HENDERSON, JJ., concur in part and dissent in part.In 1983 the legislature amended this statute to read as follows:
No previous conviction for, or plea of guilty to a violation of § 32-23-1 occurring more than five years prior to the date of the violation being charged may be used to determine that the violation being charged is a second, third or subsequent offense.
1983 S.D.Sess.Laws ch. 244, § 2.'